US 3207304 A
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United States Patent 3,207,304 METHOD OF CONCENTRATING FLUORSPAR ORES Clarence Thom, Denver, (3010., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Nov. 15, 1962, Ser. No. 237,818 2 Claims. (Cl. 2099) This invention relates to an improved method of recovering fluorspar ores and more particularly to an improved froth flotation process including a more economical depression and separation of calcite, quartz, metal oxides and other calcareous and siliceous gangue minerals with which fluorspar is generally associated.
The generally accepted method of the prior art comprises the pre-mixing of the ground ore with water and certain flotation agents, a step referred to in the art as conditioning, for various lengths of time after which the conditioned pulp is subjected to flotation to produce a froth concentrate of the valuable fluorite minerals and a non-floating product containing the undesirable impurity minerals which are discarded as waste failings. These prior art methods also require control of the pulp temperature and the addition of substantial amounts of heat to render the reagents more effective. Additionally, these processes require the removal of practically all of the soluble hardness forming salts from the water used in the process.
The conditioning is usually accomplished in an agitation tank which receives the ground ore pulp at a specified water to solids ratio, the water having been previously softened. The heating of the reagentized pulp in the conditioner tank or in the flotation machine is generally accomplished by means of the injection of live steam or by means of external heating units.
The costs of water treating and heating of the pulp in these prior art processes are undesirably high and are therefore wasteful. Further, the general practice of the depression of the impurity minerals at the alkalinity desired in the flotation operation and in the presence of the alkaline reagents in the pump is considered both wasteful and expensive.
Contrary to prior art teachings, it has been found that the separation of fluorite from impurity minerals by flotation and, more particularly, the separation of fluorite from calcite and siliceous impurity minerals can be more effectively accomplished when the conditioning of the pump is carried out at a lower degree of alkalinity than is necessary for the subsequent flotation.
Further, in contrast to the prior art methods, the method of the instant invention does not-require the addition of heat to the slurry under the novel conditions of operation. Also,fewer flotation cells are required to eifect efficient recoverysince the flotation is more rapid and complete and the depression of the calcite is also more positive and complete than in prior art processes.
In accordance with the invention, the improved method of concentrating a fluorspar ore comprises the steps of comminuting the ore, forming an aqueous slurry of the comminuted ore, adding a depressant reagent for impurity minerals to the slurry, conditioning the slurried ore at a lower alkalinity than that required for subsequent flotation of fluorite, raising the alkalinity of the conditioned ore slurry, adding a collector reagent thereto and subjecting the resulting slurry to flotation in order to recover the fluorite values as acid grade fluorspar.
It is an important object of the present invention to provide an improved method of concentration of fluorspar from ores containing impurity minerals by means of which acid grade fluorspar can be commercially produced with greater economy both in reagents and heat requirements.
A further important object of the present invention is to provide an improved method of concentrating fluorspar ores containing impurity minerals in which the ore conditioning step is carried out at lower alkalinities than that considered essential for a subsequent flotation step.
Another object of the present invention is to provide an improved method of concentrating fluorspar ores at temperatures which ordinarily do not require the addition of heat to the system.
Another object of the present invention is to provide an improved method for the concentration of fluorspar ores containing impurity minerals by means of which acid grade fluorspar can be commercially produced without requiring complete water softening of water used in the process.
A further object of the present invention is to provide an improved method for the concentration of fluorspar ores containing impurity minerals which is more efficient and economical than processes used heretofore requiring substantially less flotation equipment for the same ore treating capacity.
Another and further important object of the present invention is to provide an improved method for the concentration of fluorspar ores containing impurity minerals wherein the alkalinity of the pulp water is controlled in the conditioner and raised in the flotation machines.
A still further object of the present invention is to provide an improved method for the concentration of fluorspar ores containing impurity minerals which includes the step of pre-conditioning the ore pulp in the conditioner with an impurity depressant reagent before the addition of promoter reagents and pH modifying agents.
For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.
In the drawing, the sole figure is a self-explanatory flow diagram of a fluorspar concentrating process according to the invention.
It has been discovered that a more economical depression and separation of calcite, quartz, metal oxides and other calcareous and siliceous gangue from fluorspar ores can be made, and at lower than normal temperatures, provided the pulped ore is pre-conditioned with an impurity depressant reagent at an alkalinity less than flotation alkalinity prior to the introduction of promoters and pH modifying agents.
It is a standard in the prior art that the depression of impurity minerals in the concentration of fluorspar ores is invariably accomplished at the alkalinity desired in the flotation operation and in the presence of the alkaline agents in the ore pulp. It is discovered that this is not only wasteful of reagents but also adversely affects the recovery of the values.
It has also been discovered that the lowering of the alkalinity in the ore pulp may be accomplished to advantage by pre-conditioning the pulp in the presence of acid forming salts which may exist to a certain degree proportionally to the hardness of the natural water used in the process which also removes the usual requirement that the water used be completely softened. On the other hand or in addition, the acidity required for lowering the alkalinity of the pulp may be obtained by the addition of mineral acids or certain acid forming salts to the ore pulp. Another very convenient method of achieving the lower alkalinity is the use of an acidulating depressing agent such as quebracho or other calcite depressing reagent which contains an amount of tannic acid to eflect all or part of the lowering of the alkalinity of the pulp to the desired level.
As shown in the drawing, the fluorspar ore is crushed in crusher 1t), mostly to 100 mesh. The crushed ore is fed into a wet grinding circuit including grinder 12. The crushed ore is slurried with water which may have hardness forming salts present not in excess of about 80 parts per million. Some softening of the water used, may be required for watens having hardness in excess of this figure. The ground ore slurry passes to a classifier 14, where the +100 mesh ore is returned to the grinder. The 100 mesh ore slurry at about 25% solids is fed to the conditioner 16. The pH of the ore pulp in the conditioner is adjusted to an alkalinity less than the alkalinity of the ore to be used in the subsequent flotation operation. The alkalinity ditference may be as great as several tenths of a point of pH to as little as one tenth of a point depending on the particular ore, water and the like. These pH adjustments may be accomplished by or in addition to the adding of a depressant reagent. The addition of a depressant of acidic nature such as quebracho may provide all or part of the adjustment required. Other acidulators such as mineral acids or acid forming salts may be added to adjust the alkalinity of the ore pulp. The temperature of the pulp in the conditioner is maintained above about 70 F. with the injection of steam being required only when necessary to maintain the temperature. Usually, the addition of heat will be required only during the coldest parts of the year to maintain the operating temperature in this range.
After the pulp is conditioned for a time suflicient to depress the impurities, the alkalinity is then raised to the flotation pH by the addition of an alkaline reagent, such as, soda ash and the like and at the same time the promoter o-r collector agent, such as oleic acid, is added. The flotation and pH control agents are added after the conditioner, either in or just ahead of the first rougher cell. The pH of the pulp in the rougher 18 is adjusted to be in the range of from as much as several tenths of a pH point to as little as one tenth of a pH point higher than in the conditioner.
The overflow from the rougher 18 is fed to the cleaner 20 and the underflow goes to the tailings. The pH in the first cleaner cell may be slightly less alkaline than in the rougher and a pH slightly less alkaline than this is usually suitable for the remaining cleaner cells.
The overflow from the cleaner goes to thickener 22 and the underflow to tailings. The thickener underflow is de-watered in filter 24 and dried to provide an acid grade fluorspar. The over-flow from the thickener and filter is returned to the grinding circuit.
As an example of the operation of the present invention, a typical fluorspar ore having the following general composition shown in Table I was used.
TABLE I Wt. percent CaF 77.0 CaCO 15.0 Quartz 5.0 R 3.0
4; Example 1 The raw ore was sent to a jaw crusher, to a cone grinder and finally to a ball mill where it was mixed with water and ground mostly to mesh. The water used was settled and softened until it contained from 20-80 p.p.m. hardness. The slurry of ore and water passed from the ball mill to a hydraulic cyclone classifier which provides about a 25% solids slurry of 100 mesh as feed and returns the underflow to the ball mill. The feed slurry from the hydraulic cyclone is passed to an agitated conditioner provided with steam jets for regulating the temperature in the conditioner.
According to the improved method of this invention, the 100 mesh pulp was fed to the conditioner at a pH of about 7.8 to 8.4. In the conditioner 0.170 kilogram of quebracho per metric ton of ore is added to the pulped ore which is maintained at about 77 F. Nothing further is added to the conditioner and the conditioner pH is about 8.08.2. The slurry from the conditioner is treated with 0.386 kg./m.t. of soda ash and 0.270 kg./m.t. of oleic acid as it enters the first rougher cell. The pH in the first rougher cell is 8.4-8.6. In the rougher cells the fluorspar floats to the top with the froth and the gangue falls to the bottom and is discarded. The froth from the rougher cells flows through a launder to a four stage cleaner circuit that further separates the fluorspar and the gangue. The fluorspar concentrates are sent to a thickener where the fluorspar settles. The thickened concentrate is de-watered to an 84-88% solids by filtration and dried. The recovery of CaF was found to be 85.6% which analyzed 97.5% CaF Example 2 An ore having the composition of Table I was comminuted, classified and slurried with water having the same hardness of Example 1. The pulped ore was introduced into the conditioner and maintained at about 77 F., however, the depressant reagent queblracho in the amount of 0.170 kg./m.t. and the promoter and pH control reagents in the amount of 0.270 kg./m.t. of oleic acid and 0.386 kg./m.t. of soda ash were all added to the conditioner simultaneously. The thus conditioned pulp passed through the balance of the circuit in the same manner as in Example 1. The recovery of acid grade CaF was 70%.
Example 3 An ore having the same composition was comminuted and slurried with a water softened to 20-40 p.p.rn. hardness. The slurried ore was conditioned as in Example 2 at a pH of 9.0-9.6 except the temperature was increased to F. The pulp passed through the remainder of the system in the standard fashion and 67.3% of the CaF was recovered which analyzed 98.3% CaF In Examples 2 and 3 where the conditioning of the ore slurry occurred in the presence of the promoter and pH control reagents, a lower percentage recovery was realized; whereas, in Example 1, where the conditioning was accomplished at a pH less alkaline than that considered practical for the subsequent flotation operation and in the absence of the promoter and pH control reagents, and the alkalinity was increased for flotation by the addition of the promoter and pH control after the conditioning step, the percentage recovery is significantly increased.
While there have been described what at present are considered to be the preferred embodiments of this invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. It is aimed, therefore, in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.
What is claimed is:
1. In a process of concentrating fluorspar ore by firoth flotation including the steps of comminuting and pulping the ore with water, pre-conditioning the pulped ore, adding a collector reagent to said ore and subjecting the pre-c0nditioned ore to a flotation operation to recover the fluorspar values, the improvement which comprises: pre-conditioning the pulped ore for a period of time with an acidulating depressing agent while maintaining the temperature above about 70 F. said acidulating depressing agent being further characterized as containing an amount of tannic acid sufficient to efiect a lowering of alkalinity of the pulp to a level of at least 0.1 pH unit below the flotation alkalinity required in the subsequent flotation operation. 2. The improvement in accordance with claim 1 wherein said acidulating depressing reagent is quebracho.
References Cited by the Examiner UNITED STATES PATENTS 2,168,762 8/39 Clernmer 209-166 2,263,552 11/41 Anderson 209-166 2,407,651 9/46 Clernmer 209166 2,410,770 11/46 Booth 209-166 2,825,45 8 3/58 Snyder 209 166 FOREIGN PATENTS 1,118,112 2/60 Germany.
HARRY B. THORNTON, Primary Examiner.
HERBERT L. MARTIN, Examiner.