Method for removing heavy metals in the manufacture of phosphoric acid
AssigneeJesa Technologies LLC
InventorsStephen Wayne HILAKOS, Anis LAKHOUAJA
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Abstract
Methods for removing heavy metals from a phosphoric acid solution produced in a wet process for manufacturing phosphoric acid, comprising treating the wet-process phosphoric acid solution with a small amount of a solid adsorbing material and a complex reagent to form a heavy metal complex-contaminated solid adsorbing material, and removing the contaminated solid adsorbing material to yield a treated phosphoric acid solution having a low heavy metal content.
Claims51
A method for manufacturing phosphoric acid from a calcium- and heavy metal-containing phosphate ore, comprising the steps of:
- (a) digesting the calcium- and heavy metal-containing phosphate ore with sulfuric acid to give an aqueous mixture of calcium sulfate, phosphoric acid, and heavy metal impurities, wherein the content of calcium sulfate in the aqueous mixture is from about 20 to about 40% weight/weight;
- (b) removing the calcium sulfate from the aqueous mixture to give a wet-process phosphoric acid solution containing from about 20 to about 45% weight/weight P2O5 and having a pre-treated heavy metal content more than about 10 mg M/kg P2O5;
- (c) treating the wet-process phosphoric acid solution with from about 0.5 to about 10% weight/weight of a solid adsorbing material and from about 100 to about 5000 ppm by weight on a 100% basis of a complex reagent to form a heavy metal complex-contaminated solid adsorbing material,
- wherein the phosphoric acid solution is maintained during treatment at a temperature between 20-60° C., wherein the temperature is sufficient to allow treatment time to be up to about 180 minutes without significant decomposition of the heavy metal complex, and wherein the amount of complex reagent added is sufficient to lower the heavy metal content by at least about 10% at the temperature maintained;
- (d) removing the heavy metal complex-contaminated solid adsorbing material from the phosphoric acid solution to yield a treated phosphoric acid solution having a post-treated heavy metal content at least about 10% lower than the pre-treated heavy metal content;
- and
- (e) wherein the treated phosphoric acid solution of step (d) is recirculated in a heat exchange apparatus, and thereby used to cool the untreated wet-process phosphoric acid solution in step (c).
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A method for manufacturing phosphoric acid from a calcium- and cadmium-containing phosphate ore, comprising the steps of:
- (a) digesting the calcium- and cadmium-containing phosphate ore with sulfuric acid to give an aqueous mixture of calcium sulfate, phosphoric acid, and cadmium impurities, wherein the content of calcium sulfate in the aqueous mixture is from about 20 to about 40% weight/weight;
- (b) removing the calcium sulfate from the aqueous mixture to give a wet-process phosphoric acid solution containing from about 20 to about 45% weight/weight P2O5 and having a pre-treated cadmium content of about 50-90 mg Cd/kg P2O5 “Z”;
- (c) treating the wet-process phosphoric acid solution with from about 0.5 to about 10% weight/weight of a solid adsorbing material and from about 100 to about 1500 ppm by weight on a 100% basis of a complex reagent, wherein the complex reagent is a di-lower alkyl dithiophosphinate salt or di-lower alkyl dithiophosphate salt, to form a cadmium complex-contaminated solid adsorbing material,
- wherein the phosphoric acid solution is maintained during treatment at a temperature between 20-60° C., such that about Y ppm of the reagent is added when the temperature of the phosphoric acid solution is about X° C. according to the formula Y=((Z-50)*5)+(0.55X2−23.8X+388), +/−35%;
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- (d) removing the cadmium complex-contaminated solid adsorbing material from the phosphoric acid solution to yield a treated phosphoric acid solution having a post-treated cadmium content at least about 10% lower than the pre-treated cadmium content.
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Dependencies are inferred from the claim text.