Process for recovering arsenic compounds by sodium hydroxide leaching
AssigneeHazen Research, Inc.
InventorsJames E. Reynolds, Enzo L. Coltrinari
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Abstract
An arsenic-recovery process primarily for use in conjunction with the hydrometallurgical processing of arsenic-containing materials for metal recovery. Arsenic is recovered from ferric arsenate by reaction with sodium hydroxide in accordance with the following general reaction: 3NaOH+FeAsO.sub.4 .fwdarw.Na.sub.3 AsO.sub.4 +Fe(OH).sub.3 During the processing of high arsenic materials such as smelter flue dust, extremely insoluble ferric-arsenic compounds are generated to immobilize the arsenic during leaching of the metals. The arsenic may be recovered in saleable form from the arsenic-containing residues by leaching with sodium hydroxide and crystallizing the arsenic salts from the leach residue.
Claims19
A process for recovering arsenic from materials containing ferric-arsenic compounds in which the arsenic is present in its pentavalent state, comprising:
- (a) leaching the material with a stoichiometric excess of a sodium hydroxide solution;
- (b) performing a liquid-solid separation on the leach materials;
- and
- (c) crystallizing the soluble arsenic salt from the liquid of step (b).
A hydrometallurgical process for recovering arsenic as sodium arsenate from residues containing arsenic resulting from the step of serially leaching various metal values while carrying ferric-arsenic compounds in which the arsenic is present in its pentavalent state undissolved in the residues, which comprises
- (a) leaching the residues with sodium hydroxide in excess of stoichiometric amounts to permit a reaction wherein sodium arsenate is formed in solution and the ferric ions are precipitated by means of the hydroxide;
- (b) performing a liquid-solid separation on the material of step (a);
- (c) crystallizing sodium arsenate from the liquid of step (b).
A process for recovering arsenic from arsenic-containing materials comprising:
- (a) oxidizing the arsenic to its pentavalent state;
- (b) precipitating the arsenic with ferric ions as ferric arsenate;
- (c) leaching the ferric arsenate with a sodium hydroxide solution at a temperature of at least about 40.degree. C.;
- (d) performing a liquid-solid separation on the leach materials;
- and
- (e) crystallizing an arsenic salt from the liquid of step (d) by evaporation.
A process for recovering arsenic as sodium arsenate from a leach residue which contains a ferric-arsenic compound wherein the arsenic is present in its pentavalent state which comprises:
- (a) leaching the residue with sodium hydroxide in excess of stoichiometric amounts to solubilize the arsenic at a temperature of at least about 40.degree. C.;
- (b) performing a liquid-solid separation on the material of step (a);
- (c) performing a vacuum evaporation on the liquid of step (b) to increase the sodium hydroxide concentration from about 55 to 80 grams sodium hydroxide per liter to about 150 to 160 grams per liter and allowing to cool to crystallize sodium arsenate;
- (d) drying the arsenate crystals without washing;
- and
- (e) fixing any arsenic remaining in the solids of step (b) by adding 20 grams ferric sulfate per kilogram of residue and neutralizing to between about pH 3.5 to 4.5 with calcium carbonate to form ferric-arsenic compounds suitably insoluble for disposal to the environment.
Dependencies are inferred from the claim text.