US 3802869 A
Description (OCR text may contain errors)
United States Patent 1191' Duane et a]. Apr. 9, 1974 [5 PROCESS FOR THE TREATMENT OF ORE 1.832,006 11/1931 Puschak et al 75/81 1 V 2  Inventors: Carl L. Duane, 625 Ocean View 642390 1900 3/ Blvd, Pacific Grove, Calif. 93950; John Windsor Chamberlin Przmary E.\'ammerEdward J. Meros deceased late of 1000 sinx Ave. Assistant E.taminerGregory A. Heller Pacific drove Calif 93950 (Peter, Atturney, Agent, or Firm-Mellin, Moore & F. Chamberlin, administrator) Weissenberger  Filed: Oct. 22, 1970 211 App]. No.: 83,018  ABSTRACT A continuous process of treating ore to recover volatiles such as mercury and by-products is disclosed, in- 75/81 cluding steps by which environmental contamination  Fieid 89 63 88 and health hazards are reduced and recovery is increased. Apparatus for practicing the process is de- 56] References Cited scribed which may be portable and self-contained and which may include a novel retort, a novel condenser UNITED STATES PATENTS and a novel system for the recycling of air and water 3,6l5,363 l0/l971 de Oca 75/81 in accordance with the process of the invention 3,037,759 6/1962 Smith 75/8l 52,120 1/1966 Absterdam 75/81 15 Claims, 9 Drawing Figures PATENTEUAPR 9 1914 3,802,869
SHEET 2 BF 6 INVENTORS CARL L. DUANE FlG 2 JOHN w. CHAMBERLIN MMWP ATTORNEYS ATENTEDAPR' 9 1914 3.802.869
sum 3 nr 6 INVENTORS CARL L. DUANE JOHN W. CHAMBERLIN v ATTORNEYS PATENYEDAPR 919M $802,869
saw u or 6 CARL L. DUANE JOHN W. CHAMBERLIN 'Illlll a INVENTORS FEG 5 I ATTORNEYS PATENTEDAPR 91am 3.802.869 sum 5 0F 6 a u INVENTORS a N g b 9 CARL L. DUANE 2 Q JOHN W. CHAMBERLIN g BY mz v ATTORNEYS 1 PROCESS FOR THE TREATMENT OF ORE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the heat treatment of ore to effect recovery of volatiles such as mercury and byproducts and more particularly to a continuous process of and apparatus for such treatment in which environmental contamination and health hazards approach minimum and recovery approaches maximum.
2. Description of the Prior Art It is known in the art to treat ores so as to recover volatiles such as mercury, sulfuric acid, and the like therefrom. The ore known as cinnabar" is the principal ore of mercury and includes mercury in the form of red mercuric sulphide. The recovery of mercury from cinnabar ore comprises the basic steps of heating the ore in air to a temperature of about 1,400F. (760C.) in
order to reduce the mercuric sulfide to free mercury vapor and sulfur dioxide and then condensing the mercury vapor to liquid mercury. I
However, while cinnabar is the principal ore of mercury it is by no means the only important mercurybearing ore. Other such ores may contain no sulphur or other acid elements,.or may contain acids other than sulphur derivatives. Substantial deposits exist of'native mercury and metacinnabarite and important quantities of mercury are found in quartz, calcite, dolomite, pyrite and other gangue materials. Significant amounts of mercury have been recovered from zinc, copper and gold ores. Many valuable acids, including some exotic elements other than sulphur, are found in mercury bearing ores. 1
In the prior art the treatment of mercury bearing ores to recover mercury therefrom has been carried out by both continuous (US. Pat. No. 1,447,888) and batch (US. Pat. No. 2,090,472) processes but none of such processes has enabled the simultaneous recovery of other products therefrom in usable form. In fact, all of the prior art processes of mercury recovery have been based on the eventual venting of air and gases to the atmosphere after the mercury vapor has been condensed therefrom with attendant contamination of the atmosphere and health hazards. In certain of such processes (U.S. Pat. No. l,728,359 and US. Pat. No. 3,037,759), an attempt has been made to reduce such contamination and health hazard by scrubbing" (i.e., washing) the gases, usually with water, prior to venting the gases from the system. However, the eventual release of the scrubbing fluid simply changes the nature of the environmental contamination without reducing the health hazard.
It is an object of this invention to treat ores in a manner recovering mercury and/or other products in usable form with substantially no contamination of the environment.
In the prior art, it has been found that one of the advantages of the batch process was the fact that a sealed retort could be used in which a partial vacuum could be established to enable more rapid and more complete removal of mercury from the ore at reduced temperatures. However, in such prior art batch process, combustion and oxidation within the retort was allowed to occur resulting in the production of undesirable oxides and recovery losses of both mercury and other elements such as sulfur.
It is thus another object of this invention to provide a continuous process and apparatus therefor, in which ore is continuously fed into an externally heated retort in which a partial vacuum is maintained and in which a controlled amount of oxygen may be established to reduce the elements to be recovered to the desired form without the occurrence of combustion within the retort.
In the continuous processes and apparatus of the prior art, the ore was moved through the system by means such as tumbling or a spiralconveyor within a tube, which means produce dust with attendant formation of undesirable oxides and flowering of the evolved mercury rendering it useless without further treatment. In addition, such dust and flowered mercury form a mud either tending to clog the mercury vapor condensing system or adding contaminants to the air and gases which are eventually vented from prior art systems.
It is thus another object of this invention to provide a method of and means for moving ore through a recovery system with reduced generation of dust.
It will be understood that the process and apparatus of this invention may be used to process deposits of ore found in heavily populated areas because of the fact that substantially no environmental contamination results from the use of such process and apparatus. When deposits of ore are found in remote and sparsely populated areas, the problem of environmental contamination is less pronounced, but the problem of installing apparatus and obtaining the supplies required to practice the process assume major proportions.
Thus, it is a still further object of this invention to provide a continuous process for recovering mercury and other elements from ore in which materials used in practicing the process of the invention are conserved by recycling them through the system and by efficient utilization of power and materials.
It is yet another object of this invention to provide apparatus for practicing the process of this invention, which apparatus consists of mobile units that may be easily transported and assembled for use in either developed by underdeveloped geographical areas.
In remote areas where pollution is not a factor, it may be unfeasible, uneconomical or unnecessary to recover acid components. Thus, the invention involves the treatment of any ore to recover at least one of the volatile components therefrom.
SUMMARY OF THE INVENTION More particularly, the process of the invention is carried out by continuously treating mercury-bearing ores or the like to recover volatiles therefrom by preheating the ore in a dehydrator and then roasting the ore in a substantially sealed retort, both the dehydrator and the retort having an outlet for gases containing vapor to be condensed to a liquid from the vapor state thereof produced by the ore treatment. The ore is first moved thru the dehydrator to preheat and to remove both all moisture and a portion of the volatiles in the ore and then the preheated ore is moved thru the retort until the ore has reached a predetermined temperature. Gas and vapor are pumped from the dehydrator and the retort through a sealed vapor condensing system to establish a partial vacuum in the dehydrator, retort and condensing system and the level of oxygen in the gas present in the retort is limited to preclude combustion within the retort. The incoming ore is introduced into the dehydrator and retort and spent ore is discharged from the retort in a manner enabling the partial vacuum in the system to be maintained.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan schematic view of a preferred system for carrying out the techniques of our invention;
FIG. 2 is a vertical sectional, partly schematic, view of a portion of the system of FIG. 1;
FIG. 3 is a vertical sectional, partly schematic view taken along lines 33 of FIG. 2;
FIG. 4 is a top plan view of the floor and ore conveyor means of the retort taken along lines 4-4 of FIG. 2;
FIG. 5 is a fragmentary sectional view taken along lines 5-5 of FIG. 4;
FIG. 6 is a vertical schematic representation of the condensing and gas washing portions of the system of FIG. 1;
FIG. 7 is a vertical sectional view of a condensing tank according to one embodiment of this invention;
FIG. 8 is a cross-sectional view taken along lines 8-8 of. FIG. 7; and
FIG. 9 is a schematic representation of a prepared gas flow system for a retort in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, a system 10 is shown for carrying out the techniques of the invention. Although the invention will be described hereinabove with respect to the treatment of mercury ores, the techniques are generally applicable to the treatment of any ores in which it is desired to recover volatiles therefrom.
The techniques of the invention are particularly applicable to the treatment of cinnabar ore, a native red mercuric sulfide that is the principal ore of mercury. Very substantial deposits exist in California, some of which have been worked for almost 200 years. Of the 6 million pounds of mercury used annually in the United States, about 3.5 million pounds are imported and the balance is mostly recovered in the crude rotary furnaces internally fired with oil of the prior art. The mineral vapors, soot and other products of combustion pass into a lengthy series of condensers according to the prior art and upwards of forty percent of the mercury and all of the acids are lost and become dangerous pollutants.
These inefficiencies, the large investment required in an inflexible plant and high labor costs of the prior art have resulted in concentration of production at a few very large deposits, while hundreds of other large and medium deposits remain dormant, but available. According to one embodiment of the invention an almost fully automatic system, as described herein, may be provided for recovering mercury and sulphuric acid from cinnabar ore, with virtually no loss of mercury and no air or ground pollution.
Ore Crusher like so that it can be moved readily from site to site.
Thus, a first trailer 11 may include therein suitable ore crushing equipment 12. A raw ore feed bin 13 may also be disposed on trailer 1 l in communication with equipment 12. Such equipment 12 and feed bin 13 may include but is not limited to conventional equipment such as a jaw crusher, a hopper and feedplate, transfer conveyor, metal detector, screen, cone crusher, discharge conveyor, control panel, etc., all well known in the mining art and forming no part of the invention except as a source of ore of the proper dimensions. Thus, further description thereof would appear to be unnecessary with only discharge conveyor 101 being shown.
Power Power for the system 10 may be disposed on a second trailer 15 or the like, the trailer 15 including thereon conventional power equipment such as a diesel enginegenerator set 16, a heat recovery unit 17 coupled thereto, unit 17 including supplemental firing therein, an absorption cold generator 18, a cooling tower 19, an auxiliary generator 20, an air compressor 21, a distribution, control and switchgear panel 22 and a fuel day tank 23. All of the foregoing conventional elements are appropriately operatively engaged with each other and the processing portion of system 10 for supplying power thereto and also do not form any portion of the invention except as a source of power in various forms as described.
Processing Station A third trailer 24 is provided and includes thereon the novel features of the invention. The dotted lines indicate a foldout ore feed bin 102 in communication with the conveyor 101 from trailer 11. One or more vacuum cone stationary retort chambers, two being preferred (i.e., retort chambers 106 and 106a) are disposed on trailer 24 and interconnected by suitable conduits as will be discussed further hereinbelow.
A mercury condensing and gas scrubbing section 29 is associated with the retort chambers 106 and 106a, with suitable conduits 129 coupling both retorts to each other and to section 29. The elements of section 29 are interconnected in a manner to be discussed further hereinbelow. Also included in section 29 is both an oxygen injection and control section and an acid catalyst and concentrating section as will be discussed further hereinbelow. A master control panel 35 is dis posed on trailer 24. The interaction of all of the fore going and their operation will be described further hereinbelow with respect to the remaining figures of the drawings.
Control-Communications-Service A fourth trailer 36 is preferably disposed adjacent trailer 24 and includes thereon a control and monitor console 37 adjacent and interconnected to the master control panel 35 on trailer 24. A suitable office and locker room 38, service and maintenance shop 39 and control room 40 may also be disposed on trailer 36, the various features thereof again forming no part of the invention and being merely conventional equipment for carrying out the subsequent novel features of the invention.
Fuel Supply A fifth trailer 41 may be provided carrying thereon a suitable fuel supply, as for example, trailer 41 being a standard 5,000 gallon diesel fuel trailer with a conventional transfer pump (not shown) for transferring fuel from trailer 41 to trailer 15.
Other auxiliary trailers or the like may be provided depending on the location of the ore supply, such as trailer 42 which may include a concentrated acid storage tank 43 thereon. Personnel housing (not shown) may also be provided.
In all of the foregoing, the ore crusher trailer 11 and the power trailer include standard industry components suitable for the requirements of the ore processing. The invention disclosed herein is not dependent upon any particular method or type of ore crushing or source of power or thermal exchange and any suitable means may be provided.
Thus, for example, some mine sites may have tailing dumps of cinnabar ore of a size ideal for direct feeding into retort chambers 106 and 106a without the necessity of prior crushing. Hundreds of thousands of tons of good grade ore of this character may thus. be readily available for processing in accordance with the techinques of our invention.
As will be discussed further hereinbelow in more detail, retorts 106 and 106a may be heated by any suitable means, either electric power as disclosed, or oil or gas, with the elements of section 29 cooled by air or surface or well water. Although the process of our invention will be described with the concurrent recovery of acids from the ore, such recovery is not necessary and these acids may be wasted or discharged to the atmosphere without affecting the basic operation of our invention. Similarly, acids could be recovered according to the teaching of our invention with condensed volatiles being wasted or discharged.
DESCRIPTION OF THE PROCESSING STATION Referring now to FIGS. 2 and 3, the specific features of retort chamber 106 of the processing station on trailer 24 will now be described in detail, such features being also applicable to retort chamber 106a. The upper portion 44 of feed bin 102 is adapted to fold along dotted line 103. Dotted line 104 indicates a minimum ore level line as will be explained further hereinbelow. A conventional ore level alarm signal 105 may be provided to indicate the level of the ore in feed bin 102. A retort feed chute 107 is in communication with feed bin 102. Insulation 108 is provided about retort chamber 106 and the lower portion of feed bin 102.
An adjustable ore feed gate 109 (FIG. 2) is provided at the bottom of chute 107. An ore heating pan 110 is disposed across the extent of retort chamber 106. A plurality of radially extending curved ore movement arms 111, as shown more particularly in FIG. 4, are disposed above pan 110 and entirely submerged in the ore disposed on pan 110. An ore level adjustment rod 112 (FIG. 2) is connected to feed gate 109 and extends through the insulation 108 of chamber 106. Similarly, an ore level adjustment rod 204 is connected to a discharge gate 203 and extends through insulation 108. Electric heating elements 113 are disposed below pan 110.
A drive cap 114 is connected to both arms 111 and a drive shaft 1 15 (FIG. 3). Means 116 may be provided at the bottom for adjusting the vertical extent of shaft 115 and thus also the clearance of arms 111 within pan 110. The shaft 115 is driven by a variable speed motor 128 through appropriate drive means such as a chain and sprocket arrangement for example. Observation ports 117 may be provided extending through the insulation 108 of retort chamber 106 for viewing the interior thereof.
An ore discharge slot 118 (FIG. 2) extends from communication with the ore on pan to a dribble bucket 120. A hinged scraper 119 is associated with slot 1 18 in pan 1 10 for directing spent ore into slot 1 l8, and thus into bucket 120, after such ore has been carried in a complete circuit of the pan 110 by the arms 111. A weight-actuated gate level 121 closes the bottom of bucket and is gravity-actuated by the weight of ore thereon, which weight of course can be preset as desired.
' A heat reflector 122 is disposed below heating elements 113 and above the bottom wall of retort chamber 106. An ore discharge chute auger 123 is preferably associated with the ore exiting through bucket 120, past lever 121- and into the auger housing 1230. A variable speed driver motor 128 is preferably coupled to auger 123 for driving auger 123.
As shown in FIG. 3, conventional oxygen analyzers 124 may be associated with a valve-actuated air intake 127 communicating with the interior of retort chamber 106. Suitable controls 125 and vacuum balance valves 126 may also be provided and adapted to be actuated by analyzers 124. A vapor discharge tube 129 is in communication with the interior of retort chamber 106 opening adjacent the top of retort feed chute 107.
Referring once again to FIG. 2, a vapor trap is disposed in the feed bin 102 above chute 107. An inverted V-shaped channel member 176 (see FIGS. 2 and 3) forms the vapor trap, a gas inlet tube 207 opens into the trap under member 176 and vapor discharge tube 181 extends from trap (i.e., the space under shield 176) and merges with vapor discharge tube 129 from retort 106 for connection to condenser 131a as best seen in FIG. 6. Clean-out ports 178 may be disposed in the various vapor discharge tubes 129, 181. A flexible expansion seal coupling 182 is disposed between bin 102 and chute 107. Either oxygen or an inert gas, as required, may be supplied to controls 125 of air intake or pressure reducing gas inlet 127 from an appropriate supply tank 184)). Spent ore may be drawn off from the housing of auger 123 through outlet 187.
A graphite lubricator and seal 191 may be provided about the lower end of arm drive shaft 115. The dotted line 193 represents the ore level which is maintained in the ore heating pan 110. The throat 194 of the ore bin 102 is preferably made of inconel or similar material. Stays 195 support bin 44 in its open unfolded operative position. Legs 196 support the ore pan 110. A vacuum balance valve 126 is disposed in tube 181 and a vapor cut-off valve 201 in tube 129. Electric power connection may be made through box 192 as desired. Steel support members 179 support the entire ore bin 102.
The movement of the ore through the retort 106 will be more fully understood by reference to FIGS. 4 and 5. As shown in FIG. 4 the arcuate ore movement arms are caused to rotate on the ore heating pan 110 in a clockwise direction by the arm drive cap 114 passing over the ore discharge slot 118 and under the ore inlet chute 107.
Referring to FIG. 5, it will be seen that the ore impeller arms 111 are at all times submerged beneath the normal ore level represented by line 193. Such ore level is maintained by the feed gate 109 associated with the inlet chute 107 and by the discharge gate 203 associated with the discharge chute 118. As shown in FIG. both the feed gate 109 and the discharge gate 203 have ore level adjustment rods 112 and 204 respectively associated therewith to enable the level of the ore to be adjusted. Such adjustment rods extend through the walls of the retort 106 and are adapted to be extended or retracted to cause the gates 109 and 203 to rotate about their hinged mountage. it will be seen that the feed gate 109 is shown in position for establishing a very'low ore level. To establish the ore level represented by line 193 the adjustment rod 112 would be retracted causing the gate 109 to pivot upwardly about its hinge mounting until the free end of the gate 109 substantially coincides with the normal ore level 193. The discharge gate 203, however, is shown in its normal position for maintaining the normal ore level 193. The extention of the adjustment rod 204 will tend to result in a lower ore level while the retraction of the adjustment rod 204 will tend to result in a higher ore level. The member 119 associated with the inlet chute 107 serves to scrape spent ore off of the top of the impeller arms 111 so that spent ore will not be reintroduced into the heating cycle.
As best shown in H6. 5,' the impeller blades are faced with a very hard heat resistant material as by bolting a strip 111a of tungsten carbide to the front of the arms. Such strip serves to crush the ore as it is moved along the surface of the pan 110. As also shown in FIG. 5 heating elements 206 together with heat reflectors 206a may be provided above the normal ore level to provide more even heat distribution within the retort 106.
Referring now to FlG. 6, 7 and 8, the gas scrubber section 29 of the processing station on trailer 24 will be described in detail with further reference to the retort chamber 106 of FIGS. 2 and 3 where applicable.
An insulated chill room 130 comprises the housing for the condensers 131 (three such condensers 1314 through 131C being shown). lt is to be noted that, for convenience of illustration. all of the condensers to be described hereinbelow are shown as disposed in a linear arrangement in FIG. 6 with respect to the remaining tanks in room 130. However. in a particular embo'diment of our invention, the. condensers and tanks are preferably arranged as shown schematically in H6. 1. 'A generally vertically disposed tube 132 extends centrally through each condenser 'l31a--131c. These tubes are made of a metal not subject to attack by the volatiles being recovered. Thus, each condenser is an essentially annular conduit through which the vapor laden gas is caused to pass upwardly in a preferably helical path as indicated by the arrows. As illustrated, the vapor discharge tubes 129, 181 communicate with the first condenser 131a at the bottom thereof. Connecting tube 133a communicates between the top of condenser 131a and the bottom of condenser 1311b. Similarly, connecting tube 133); communicates between the top of condenser 131b and the bottom of condenser 131a. Thus, the vapor laden gases pass through each of the condensers 131a-13lc in series.
Referring to FIGS. 7 and 8 cross-sectional views of a condenser 1310 showing one embodiment thereof in accordance with the invention are shown. According to the embodiment of the invention the tube 132 is hollow and serves as an evaporator of the refrigeration system. Thus, liquid refrigerant from the appropriate supply unit is fed into the bottom of the tube 132 through an appropriate line 212 and valve 213. The refrigerant absorbs heat from the gas and vapor present in the condenser 13la and the expanded vapor exits through the line 215 at the top of the tube 132 and is returned to the refrigeration unit to be recompressed. Thus, a low temperature source is provided along the center line of the condenser 131a.
As mentioned above, the gases and vapor are introduced into the bottom of condenser 131a through conduit 129 and exit from the top condenser 131a through connecting tube 133a in such a way as to cause the gas and vapor to cyclone (i.e., follow a helical path) upwardly therethrough about the tube 132. It has been found that mercury vapor will not condense out of a gas flow efficiently regardless of the temperature of such gas flow unless it impinges on a metal surface. Thus, the cyclone action causes the gas and vapor to tend to remain in continuous contact with the cooled metallic outer wall of the condenser 131a. In addition, according to this embodiment of the invention, the tube 132 is supported centrally within the condenser 131a by means of a plurality of metallic rods 132a extending radially outward from the tube 132 to the outer wall of the condenser 131a and arranged in a spiral along the length thereof thus providing a helical path therebetween corresponding to the helical path followed by the gas and vapor passing through the condenser 131 a. Such metallic rods 1320 thus tend to create turbulance at the boundaries of such helical path and not only serve to aid in the extraction of heat from the gas and vapor but also provide additional metallic impingement surfaces to aid in causing condensation of the mercury vapor. Other structures could, of course, be used which would provide the required cyclone action and turbulance within the condenser to ensure maximum impingement of the mercury vapor on cooled metallic surfaces in accordance with this invention. For example, the rods 132a might be replaced by elongated wire mesh or screen member arranged in a spiral within the annular space between the tube 132 and outer wall of the condenser 131a.
Referring again to FIG. 5, a plurality of water spray nozzles 134 are disposed at the top of chill room opening along the entire upper extent thereof and onto the condensers 131 in room 130. A chill water supply line 135 is coupled to nozzles 134 while a chill water return line 136 extends from a chill water pan 137 at the bottom of chill room 130. Lines 135 and 136 are appropriately connected to a source of chilled water at a temperature of about 40F as, for example, a system including cold generator 18 and pumps for recirculating cold water through the system.
lt should be understood that the chill room 130 could also be cooled by other means in accordance with this invention. For example, the expansion elements of the refrigeration system might be located within the chill room 130 in direct contact with the condensers 13la-131c. The chill room must, of course be appropriately insulated but any method of providing a low temperature within the chill room and efficient extraction of heat from the condensers and other tanks located in the chill room 130 may be used in accordance with this invention.
Mercury discharge lines 138a-138c extend from the bottom of condensers 131a-l31c respectively and open into a mercury accumulator 139. An auger is disposed longitudinally of accumulator 139 with a variable speed drive motor 141 connected to one end thereof. A source water inlet line 142a opens into one side of accumulator 139 with dilute acid water discharge line 143a opening out the other side thereof. A clean-out plug 144 may be disposed at the bottom of one side of accumulator 139. A mercury P-trap 145 is disposed at the bottom of the other side of accumulator 139. Dilute acid water discharge line 143a opens into an amalgamator 146 which is disposed adjacent accumulator 139. Flexible paddles 147 are disposed in amalgamator 146 actuated by a variable speed drive motor 141a. A mercury recording meter 148 is associated with the mercury P-tray 145 and opens into an appropriately sealed mercury storage vault 149 with an appropriate normally closed and sealed outlet 149a. A like mercury P-trap 145 extends from amalgamator 146 and is coupled to the mercury recording meter 14 and in turn to mercury storage vault 149.
A dilute acid water discharge line 143b extends from the amalgamator 146 through pump 1430 and filter 143d to the dilute acid water storage tank 153 disposed below the chill room 130. A recirculating acid water pump 151 is connected to the dilute acid water storage tank 153 and serves to pump dilute acid water out of the storage tank for utilization in the system as will be more fully described hereinafter.
The remaining tanks in the left hand side of the chill room as shown in FIG. 6 are primarily designed for the treatment of the gases remaining after the mercury vapor has been condensed therefrom. However, small amounts of mercury will be condensed in such tanks and conducted from the bottom thereof to the mercury storage vault 149 by a line 145b which joins the metcury line from the amalgamator 146.
Thus, a catalyst tank 155 is disposed in the chill room 130 and is connected to the condenser tank 1310 by connecting tube 1330 extending from the top of condenser 1310 to the bottom of tank 155 as shown. A plurality of generally horizontally extending vertically spaced catalyst trays 157 together with appropriate heating means 156 are disposed at the bottom of tank 155. Such catalyst trays 157 may comprise sieve like pans each carrying a quantity of vanadium pellets, for
example. A service panel 158 in the wall of tank 155 is preferably associated with the trays 157 and heating means to enable servicing thereof.
An acid concentrating tank 163 is disposed in the chill room and connected to the catalyst tank 155 by tube 133d extending from the top of catalyst tank 155 to about the middle of acid concentrating tank 163. An acid water spray line 151a connects the pump 151 to spray nozzles 134a located near the top of acid concentrating tank 163. Thus, after interacting with the catalyst in tank 155, the gases are caused to flow upwardly through tank 163 against a downward spray of dilute acid from nozzles 134a resulting in concentrated acid which is collected in the bottom of tank 163. An acid P-tray line 159 connects the bottom of tank 163 to the pump 151 through a means 154 for sensing the specific gravity of the acid and an appropriate filter 152. Thus, a control 160 at the inlet side of pump 151 enables a quantity of dilute acid water to be pumped from storage tank 153 and sprayed through nozzles 134a within tank 163. When sufficient dilute acid has accumulated in tank 163 to fill the P-trap 159, a flow of acid will occur through the P-trap as well as associated means 154 for measuring specific gravity and filter 152 to the inlet of pump 151. Control 160 will then disconnect the pump from the storage tank 153 and the accumulated acid will be recirculated through the tank 163 until a preselected level of concentration is measured by means 154. The means 154 will then actuate controls 160a, 1601) and 1600 connecting the pump 151 to a concentrated acid discharge line and by passing the acid P-trap 159 to enable the accumulated and now concentrated acid to be pumped from the tank 163 into a concentrated acid storage tank represented at 162. Controls 160, a, 160b and 1600 are then reversed so that a new charge of dilute acid is pumped from storage tank 153 into concentrating tank 163 through nozzles 134a and the cycle is repeated. It is noted that a continuous flow of mud filtered from the acid by the filter 152 will issue from filter discharge 152a for disposal.
A decontamination tank 164 is located in the chill room 130 and the top of the acid concentrating tank 163 is connected to the bottom of the decontamination tank 164 through tube 133e, vacuum pump 165 and tube 133 Fresh water from inlet 142 is introduced into decontamination tank 164 through a make-up water control system 169, system water pump 168, filter 152b and spray nozzles 134b. Thus, the gasses pumped from the system by vacuum pump 165 are directed upwardly in tank 164 against a descending spray of fresh water to remove any contaminants that may remain in such gasses. The water introduced into tank 164 through nozzles 134i; is pumped from the bottom of tank 164 by pump 161, through a water recovery tank 167 and back to the make-up water control system 169 for reuse. A valve-actuated clean-out drain 166 is preferably provided in the bottom of tank 164 and a drain 1520 is provided in filter 152b for clearing the water system of solid materials.
A gas outlet tube 174 extends from the top of tank 164 and includes a branch portion 174a controlled by an air return valve 170. A relief valve 171 may be disposed in main line 174 to provide a valve-actuated exhaust stack 175.
Oxygen may be supplied to the gas entering tank 155 from an oxygen supply tank 184 and line 184a connected thereto extending into gas flow communication with connecting tube 1330. An oxygen analyzer 124a may extend between tank 184 and tube 1330 as illustrated. Suitable oxygen control may also be provided as at control 125a in operative engagement with tank 184. Tube 132 and metallic vapor impingement means 132a may also be associated with tanks 155, 163 and 164 as discussed with respect to condenser 131a and to the extent of each tank as illustrated.
Operation in operation of the complete plant, raw ore is moved from the crusher trailer 11 into feed bin 102 through conveyor 101. Preferably, the ore is crushed to a maximum size of about three-fourth inches. Electrical and thermal power is supplied by trailer 15 as discussed previously. The engine-generator set 16 supplies electrical power to crusher trailer 11 and to the main processing trailer 24 through distribution and control panel 22. Exhaust heat and hot jacket water from set 16 runs into heat recovery unit 17 which converts the waste heat into low pressure steam. This low pressure steam operates the absorption cold generator 18 which produces chilled water to cool the chill room 130 on processing trailer 24 (suitable connections therebetween not shown). Auxiliary apparatus for generator 18 is the cooling tower 19.
With the above apparatus, the waste heat, from the production of the electric power required to heat retort chambers 106 and 106a and operate the various motors, is used to cool the mercury and acid and make possible their efficient and rapid recovery. The diesel fuel day tank 23 is connected to the heat recovery unit 17, to the auxiliary electric generator 20 and air compressor 21 and to the main diesel engine generator set 16. Fuel tank 23 is in turn connected to the main diesel fuel supply on trailer 41.
The generator of set 16 supplies power to the panel 22 from which it flows through suitable connecting means (not shown) to the other trailers and the various motors, on power trailer 15, such as unit 17, generator 18, cooling tower 19, fuel tank 23 and the various equipment therein. Exhaust heat from set 16 flows into the unit 17 where the maximum amount of heat is extracted and engine noise is muffled to aminimum level, discharging at stack 17a.
Hot jacket water flows from set 16 to the heat recovery unit 17, then returns to set 16. Steam from the heat recovery unit 17 flows to cold generator 18, with condensate water returning to the heat recovery unit 17. Warm water from the cold generator 18 flows to the cooling tower 19, and returns thereto. Chill water flows from cold generator 18 to the chill roor'nsupply line 135 on processing trailer 24, returning through chill water return line 136 to the cold generator 18 (See vFIG. Makeup water for the water cooling tower 19 of choice and forms no specific part of our invention.
The processing of the ore and the subsequent recovery of mercury and acids is accomplished entirely on the processing trailer 24, the equipment thereon being shown in detail in FIGS. 2 through 9. Theme crushed to a maximum of three-fourth in. on crusher trailer 11 is moved into the retort ore feed bin 102 by conveyor 101. The upper portion 44 of bin 102 is preferably con- I I structed to fold at 13 ft. 6 in. above ground level to permit highway travel, as at fold line 103. When in position for operation, the upper portion 44 of the bin 102 is supported by the bin stays 195, which are preferably structural steel members. The bin 102 is supported by additional steel members 1790 from the ground and around the periphery of the bin 102 to handle the ore load of over 60 tons.
The ore feed bin 102 must be filled to the critical level 104 to create a seal at all times during operation. To this end the minimum ore level 104 is always maintained in bin 102. If the ore level drops below this minimum level, alarm signal 105 alerts the operator and subsequently, if the bin 102 is not refilled, shuts off the entire plant. Heat from the retort chamber 106, which is preferably circular in the interior thereof, rises through the feed chute 107, thus preheating and dehydrating the ore in the lower portion of bin 102. This lower portion 194 of bin 102 and chute 107 are constructed of heat resistant alloy, such as inconel metal as previously indicated.
Steam and vapor rising from the lower portion of bin 102 are collected by vapor trap 176 and drawn off through tube 181 and vacuum balance valve 126 by vacuum into the first condenser 131a (FIG. 6). The discharge throat of the lower portion 194 of the feed bin 102 is connected to the feed chute 107 by the flexible expansion seal coupling 182 so as to prevent vapor from the retort chamber from escaping.
Ore flowing down through the feed chute 107 into the stationary ore heating pan 110 passes under ore feed level control gate 109 and under discharge level control gate 203 which are adjusted by rods 112 and 204 respectively under visual observation through ports 117. These ports 117 consist of a tubular member running through insulation 108, preferably having pyrex lenses at each end, and is located in the conical dome of the retort chamber 106. Pan 110 is preferably constructed of an alloy capable of operating continuously at temperatures in the range from l,l0OF. to 1,800F.
The ore impeller arms 111 are revolved slowly in a clockwise direction as'shown in the drawing beneath the ore level 193 and thus submerged within the ore causing a very gradual, dust free movement of the ore bed toward ore discharge slot 118. The ore impeller arms 111 (FIG. 4) are preferably faced with tungsten carbide strips 11a. The arms 111 are formed in an are which is preferably equal to the radius of the ore pan 110 and are bolted to the arm drive cap 114 at the hub of the drive shaft 115. This shaft 115 rotates in sleeve bearing 188 supported by collars centrally disposed in ore pan 110. Arms 111 are preferably operated at whatever variable speed may be required to bring the ore to the optimum temperature required to fully release the minerals into a vapor state before discharge of the spent ore at slot 118.
The shaft "5 is supported by thrust bearing I and by the arm/pan clearance adjustment means 116. The
interface between the shaft 115 and the bearings is the graphite lube and seal 191. Shaft 115 is preferably driven by variable speed drive motor 128, which may have a chain and sprocket drive.
Electric heating elements 113 are firmly affixed to the bottom of ore heating pan and are connected through power connection 192 (such as a plug) to the generator set 16 on trailer 15 through the control panel 22.
Heating elements 113 are controlled by zone pyrometers (not shown) on the control panel 35, which elements also control variable speed arm drive motor 128, to insure that all ore reaches an optimum mineral release temperature, e.g., 1,400F., before arrival at discharge slot 118. Heat from elements 113 is reflected upwards by reflectors 122. The entire retort chamber 106 is covered with high temperature insulation 108 and is supported by the legs 196 which are attached to the bed 177 of trailer 24.
Spent ore, including that scraped off the top of arms 1 1 1 by scraper wall 119, drops into chute 1 18 which is connected to dribble bucket 120. The ore maintained in the dribble bucket acts as a constant closing seal to enable a partial vacuum to be maintained within the retort chamber 106. The dribble bucket closure member is the dribble bucket gate and lever weight 121 which is adjusted to retain sufficient spent ore in chute 118 to effect a positive seal in the outlet of spent ore from the retort chamber 106. Spent ore drops from the dribble bucket 120 into auger housing 123a which is also a discharge trough from which it is moved to the tailings dump outlet 187 by auger 123 which is driven by variable speed drive motor 128.
Gases are pumped from the retort 106 through the condensers 131a131c, catalyst tank 155, and acid concentrating tank 163 by vacuum pump 165 and may be returned to the retort chamber 106 through decontamination tank 164, return valve 170, inlet 127 and retort vacuum balance valves 126. Such gas flow causes the mineral vapors rising from the heated ore bed in pan 110 to be drawn by vacuum from retort 106 into the vapor discharge tube 129 and then into condenser 131a, etc., through vapor cutoff valve 201.
Tubes 129 (FIGS. 2 and 3) are fitted with cleanout ports 178 for service purposes. The vapor flowing through tube 129 is drawn into condenser 131a which is located in chill room 130 (FIG. 6). Impingement rods 132a are located in condenser 1310 to cause the mercury vapor to liquify and flow down through mercury discharge line 138a into accumulator 139 below the water level 198 therein. Vapor flows from tank 131a by vacuum through connecting discharge tube 133a into condenser 131b, where it is again subjected to the action of the impingement rods 132a, discharging liquid mercury through outlet 138b into the accumulator 139 below the water level 198. This process is repeated in condenser tank 1310 and all of the mercury thus collected is washed in the accumulator 139 by the rotation of auger 140 in water entering through inlet 142a, the flow of which is controlled by valve 200. Accumulator 139 is preferably mounted at a slight angle from the horizontal and is generally U-shaped in cross-section with auger 140 rotating in its lower portion.
The mercury collected in the bottom of accumulator 139 as indicated by dotted line 197 flows through P- trap 145 and mercury recording meter 148 into the mercury vault 149. The water flowing into the accumulator 139 absorbs the acids entering from the condenser tanks l31a-131c and is discharged through outlet 143a into the amalgamatos 146. The mercury and any solids which are carried into the amalgamator 146 with the water are scrubbed by flexible paddles 147, after which the dilute acid water passes through outlet l43b through pump 143c and filter 143d into the dilute acid storage tank 153 and the mercury through P-trap 145 and meter 148 into the mercury vault 149. The accumulator 139 and the amalgamator 146 are each driven by variable speed drive motors 141 and 141a, respectively, which may be adjusted to suit the character and flow rate of the ore being processed.
All of the mercury and acid recovery tanks are located in the chill room 130 which is insulated and supplied with chilled water, preferably at F, by the cold generator 18 on trailer 15, through supply line 135 and spray nozzles 134 which spray the exterior surface of tanks 155, 163 and 164 and condensers 131a-131c. The chill water returns to cold generator 18 through line 136 which drains pan 137.
The vapor flowing from the tank 131a into tube 1330 is sampled by oxygen analyzer 124a which causes oxygen control l25a to add the amount of pure oxygen from supply 184 to the vapor required to combine with the sulphurous vapor to effect the recovery of sulphuric acid. The oxidized vapor then passes into the catalyst tank where it flows through the catalyst trays 157, which are preferably made of stainless steel screen and support vanadium pellets. The vapor then flows into the acid concentrating tank 163 above the upper level 199 of dilute acid accumulated therein where it moves upward against a down-flow of dilute acid spray from spray nozzles 134a.
The vacuum pump 165 draws the remaining gas through tube 133e and forces it into the final decontamination tank 164 under pressure, upward against a downflow spray of water from nozzles 134b. Any residual contaminants are removed through cleanout 166. The gas then flows out tube 174 and into portion 174a and through air return valve back to the retort chambers 106 and 106a (FIGS. 2 and 3).
The dilute acid is drawn from the storage tank 153 by acid pump 151 and sprayed into the acid concentrating tank 163 through nozzles 134a, downward against the uptlowing vapor. The tank 163 fills with acid until level 199 is reached, at which time it activates acid P-trap 159 whereupon on the acid pump 151 recirculates the dilute acid continuously until it has absorbed sufficient of the acid vapor to activate the specific gravity control 154. This indicates that the acid is now concentrated to the required commercial grade, at which time it is discharged into the concentrated acid storage tank 162. Thereafter, another batch of dilute acid is run into the concentrating tank 163 and the process is repeated.
Tube 129a may extend from tube 129 to the second retort chamber 106a (FIG. 1). Finally, although water has been suggested as the cooling medium, any suitable cooling fluid, such as air or a refrigerant, may be used.
Combustion within retort chamber 106 is prevented by selectively controlling the content of oxygen therein through the oxygen analysers 124 and the controlled inlet 127. Although an oxygen supply 18412 may be associated with analysers 124 and inlet 127, it may be necessary to provide a source of a suitable gas such as nitrogen instead in order to reduce the oxygen content in chamber 106; that is, provide sufficient oxygen to support the desired reaction but not enough to support combustion.
Referring to FIG. 9 a preferred gas flow arrangement for a retort in accordance with this invention is shown. According to this arrangement a portion of the cooled gas which is returned to the retort 106 through return line 127 is tapped off of the main line ahead of the oxygen control means 125, 184 by a pair of branch lines 207 and 209. Branch line 207 conducts the cooled gas directly to the vapor trap under the inverted V-shaped channel member 176 through a valve 208 and mixing chamber 211. Branch line 209 conducts the gas first into heat exchanging relationship with the retort 106 and then through a valve 210 to the mixing chamber 211 for introduction into the vapor trap under channel member 176. Thus, the gas in branch 209 may be heated to a temperature approaching the temperature of the retort 106 prior to being introduced into the vapor trap. Thus, by manipulation of valves 208 and 210 the cool gas from branch 207 may be mixed with the heated gas of branch 208 in mixing chamber 211 to provide gas at a selected temperature for introduction into the vapor trap under channel member 176. In this way the preheating of the incoming ore in the throat of bin 102 immediately prior to entering the inlet chute 107 may be controlled to insure complete dehydration of the ore and removal of the optimum amount of other volatiles from the ore prior to exposing the ore to retort temperatures. In addition, the introduction of gases at controlled pressures into the vapor trap will insure correct gas flow characteristics in accordance with this invention.
Summary By the process and apparatus of our invention as described hereinabove, crushed ore is moved through externally heated retorts in an uncontaminated, dust free atmosphere, under a partial vacuum, until the ore has reached the optimum temperature required for vaporization of the minerals. The retort chamber feed is sealed, to enable the partial vacuum to be established, by preheated crushed ore. The retort chamber is similarly sealed at the discharge by waste material from which the minerals have been extracted. The vapor is moved under vacuum into a condensing system in which the mercury is liquified and removed. The residual acid vapor is drawn through a catalyst into a scrubbing and concentrating tank. The concentrated acid is removed to storage and the decontaminated air passes through a vacuum pump and is returned to the retorts or vented to the atmosphere.
Among the important features of our invention, but not limited thereto, are the following:
The air intake into the retort chamber is controlled both qualitatively and quantitatively and a partial vacuum is maintained therein at all times. The preheating of the ore'prevents thermal shock to the ore bed plate when the ore enters the very hot retort chamber. The means for removing acid from the vapor, processing and concentrating it by injecting oxygen into the vapor after the mercury is removed and the vapor passed through a bed of catalyst into a recirculating spray of initially dilute acid water, creating commercial grade sulphuric acid, is an important feature. The means for decontaminating the air and recirculating it to the retort so as to prevent oxygen from entering the retort to cause formation of oxides resulting in recovery losses of both mercury and sulphur is also very important.
The means for moving the ore continuously thru the retort without exposing the moving means to the atmosphere and without creating turbulenceis another important feature. If this is not done, minute particles are released from the ore into the vapor as dust which contaminates the vapor, combines with mercury in insoluable form and makes mud in the condenser. The means for controlling the speed of movement of the ore through the retort so that it reaches a predetermined optimum temperature required for complete removal of the mercury is important. Cinnabar occurs in a wide variety of formations from sandstone to agate causing varying processing time to reach the critical temperature of 1,400F. The variable speed drive for the ore movement arms is controlled by thermal means so that all ore must reach the desired temperature before it is discharged. A partial vacuum is maintained constantly on the retort, condenser and acid system. This prevents escape of vapor with consequent loss of recovery and lethal pollution and insures rapid controlled removal of the vapor to the condenser.
Mercury liquifies by a combination of cooling of the vapor and vapor striking metal surfaces. Unless the metal surfaces are constructed so that the vapor positively cannot bypass, losses will occur. The means for continuouslyaccumulating the liquid mercury and vapor-bome solid particles is an important feature. Otherwise, excessive acid mud will be formed interfering with the system operation and efficiency. Finally, the means for continuously washing and amalgamating the accumulations to remove entrained acid and mercury is important. Recovery losses and contamination occur if this apparatus is not part of the system. No other known prior art systems have means for accumulation, washing and amalgamation.
The preparation of the ore for processing in the retort chambers and condensers is done by any of many devices well known in the industry, such as jaw and cone crushers, screens and combinations thereof. It is essential to the process that the feed bin for the ore heating chambers be kept continuously filled with ore of an optimum size to a level insuring against escape of vapor from the chambers.
While the heating of the ore treatment pan may be done by gas or oil firing, a preferred method is by affixing the electric heating elements to the bottom of the pan, thus insuring exact control of temperatures at the precise locations required. Electric power is supplied by the dieselor gas-powered engine generator set 16 on power trailer 15. The waste jacket and exhaust heat from set 16 is fed into the heat recovery unit 17 to operate the cold generator 18 which produces chilled water for the mercury condensing and acid recovery systems as described hereinabove.
The above process and apparatus may be equipped with all necessary automatic and variable controls, indicator, recording, metering, safety and emergency devices to permit its operation by a single supervisory person, such controls and devices preferably being located at panels 35.
Since this is a vacuum, recirculating system providing positive decontamination and demineralization, air pollution is virtually impossible and no health hazards exist. The process and apparatus of our invention may be entirely mobile so that it may be easily transported over normal highways. One trailer may contain the power, another the ore retort chambers and the condenser system and a third may include the ore crushing and preparation equipment. Additional trailers may be provided for control, service, fuel supply and acid storage We claim as our invention:
1. In the process of continuously treating mercury bearing ores to recover volatiles therefrom wherein said ore is preheated in a dehydrator and then roasted in a substantially sealed stationary retort having an outlet for gases containing volatiles to be condensed to a liquid from the vapor state thereof produced by said ore treatment, the steps of:
a. moving said ore through said dehydrator to preheat said ore to a temperature above 212F to remove all moisture and a portion of the volatiles in said ore;
b. then moving said ore through said retort until the ore has reached a predetermined temperature above 1,000F;
c. pumping gas and vapor both from said dehydrator and from said retort through a sealed vapor condensing system to establish a partial vacuum in said dehydrator, retort and condensing system;
d. limiting the level of oxygen present in said retort to preclude combustion within said retort; and
e. feeding fresh ore into and discharging spent ore from said retort in a manner maintaining said partial vacuum therein.
2. In the process of continuously treating ores bearing mercury and sulphur to recover mercury therefrom wherein said ore is preheated in a dehydrator and then roasted in a substantially sealed stationary retort having an outlet for gases containing mercury vapor to be condensed to a liquid from the vapor state thereof produced by said ore treatment, the steps of:
a. moving said ore through said dehydrator to preheat said ore to a temperature above 2l2F to remove all moisture and a portion of the mercury in said ore;
b. then moving said ore through said retort until the ore has reached a predetermined temperature between l,OOOF and l,600F;
c. pumping gas and vapor from said dehydrator and said retort through a sealed mercury vapor condensing system to establish a partial vacuum in said dehydrator, retort and condensing system;
d. analyzing limiting the level of oxygen present, and
admitting gas to in said retort to preclude combustion within said retort; and
e. feeding fresh ore into and discharging spent ore from said retort in a manner maintaining said partial vacuum therein.
3. The process of claim 2 including the steps of analyzing the gas leaving said mercury vapor condensing system and adding a controlled amount of oxygen to said gas leaving said mercury vapor condensing system to establish the level of oxygen in said gas required to remove all sulfur products therefrom in the form of sulfuric acid.
4. The process of claim 2 wherein the step of limiting the level of oxygen includes the steps of returning gas to said retort through a pressure reducing conduit, analyzing the gas present in said pressure reducing conduit, and adding inert gas thereto in an amount sufficient to maintain an oxygen level sufficient to dissociate mercuric sulfide in said retort without the occurrence of combustion within said retort.
5. In the process of continuously treating cinnabar ore to recover mercury wherein said ore is heated to a temperature above l,000 in a retort having an inlet for said ore, an outlet for said ore and an outlet for mercury vapor to be condensed to a liquid from the vapor state thereof produced by said ore treatment, the steps of:
a. utilizing said ore to substantially seal said inlet and said outlet of said retort;
b. heating said incoming ore sealing said inlet of said retort to a temperature above 212F to dehydrate said incoming ore;
c. pumping gas from said inlet and from said retort first through a sealed vapor condensing system sealingly attached to said mercury vapor outlet of said retort and then through a sealed gas scrubbing system to establish a partial vacuum in said retort, condensing system and gas scrubbing system;
d. removing sulfur and oxygen from said gas in said gas scrubbing system in the form of sulfuric acid by exposure of said gas to a controlled amount of oxygen in the presence of a catalyst and water;
e. returning said gas to said retort through a pressure reducing conduit to preserve the partial vacuum in said retort; and
f. analyzing said gas and limiting the level of oxygen present in said gas returned to said retort to preclude combustion within said retort.
6. The process of claim 5 including the steps of wash- 5 ing said mercury condensed to a liquid from the vapor state with water and subsequently introducing said water into said gas scrubbing system.
7. The process of claim 5 including the step of impinging said mercury in said vapor state on multiple cooled metal surfaces in said condensing system.
8. The process of claim 5 including the steps of analyzing the gas entering said gas scrubbing system and adding controlled amounts of oxygen to said gas to maintain a preselected level of oxygen in said gas scrubbing system.
9. The process of claim 5 including the steps of crushing said ore to a pre-selected maximum size prior to entry of said ore into said inlet of said retort and maintaining at least a given quantity of said crushed ore in said inlet of said retort.
10. The process of claim 9 including the step of maintaining a given quantity of said ore in said outlet of said retort.
11. The process of claim 10 including the step of moving said ore from said inlet of said retort-to said outlet of said retort by applying force to submerged strata only of said ore thereby reducing the production of dust due to said movement.
12. In the process of continuously treating cinnabar ore to recover mercury therefrom wherein said ore is heated to a temperature above l,0OOF in a substantially sealed retort having an outlet for gases containing mercury vapor to be condensed to a liquid from the vapor state thereof produced by said ore treatment, the steps of:
a. pumping gas from said retort first through a sealed mercury vapor condensing system sealingly connected to said mercury vapor outlet of said retort and then through a sealed gas scrubbing system sealingly connected to said condensing system to establish a partial vacuum in said retort, condensing system and gas scrubbing system;
b. removing sulfur and oxygen from said gas in said gas scrubbing system in the form of sulfuric acid by exposure of said gas to a controlled amount of oxygen in the presence of a catalyst and water;
0. returning said gas to said retort through a pressure reducing conduit in communication with said retort to preserve the partial vacuum in said retort; and
d. analyzing said gas and limiting the level of oxygen present in said gas returned to said retort to preclude combustion within said retort.
13. The process of claim 12 including the steps of analyzing the gas present entering said gas scrubbing system and controlling the amount of oxygen added to said gas entering said gas scrubbing system to limit the level of oxygen in said gas to that required to remove all sulfur products therefrom in the form of sulfuric acid.
14. The process of claim 13 including the steps of analyzing the gas present in said pressure reducing conduit and adding oxygen thereto in an amount sufficient to maintain an oxygen level sufficient to dissociate mercuric sulfide in said retort without the occurrence of combustion within said retort.
15. In the process of continuously treating cinnabar ores bearing volatile acid forming elements wherein said ore is preheated in a dehydrator and then roasted in a substantially sealed stationary retort having an outlet for gases to be condensed to a liquid from the vapor state thereof produced by said ore treatment, the steps of:
a. moving said ore through said dehydrator to preheat said ore to a temperature above 212F;
b. then moving said ore through said retort until the ore has reached a predetermined higher temperature;
c. pumping gas and vapor from said dehydrator and said retort into a sealed gas scrubbing system to esremove all acid forming elements therefrom.