US 5,449,503 AGranted

Process for separating arsenic acid from an aqueous mixture comprising sulfuric and arsenic acids

AssigneeAlliedSignal Inc.

InventorsCharles L. Redmon, Somanahalli N. Subbanna, Robert A. Smith

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Abstract

The present invention provides a process for recovering arsenic acid from a starting mixture comprising sulfuric and arsenic acids and water. In step (a), the starting mixture is treated with a sulfur (IV) compound which will reduce the arsenic acid to arsenic (III) compound under conditions sufficient to substantially convert the arsenic acid to arsenic (III) wherein the resulting mixture comprises arsenic (III) compound, the sulfur (IV) compound, sulfuric acid, and water. In step (b), the resulting mixture is purged with gas to substantially remove the sulfur (IV) compound from the mixture wherein the purged mixture comprises the arsenic (III) compounds, sulfuric acid, and water. In step (c), the purged mixture is treated under conditions sufficient to substantially separate the arsenic (III) compounds from the purged mixture. In step (d), the separated arsenic (III) compound is reacted with an oxidizing agent to substantially convert arsenic (III) compound to arsenic acid wherein the final mixture comprises arsenic acid, unreacted oxidizing agent, and water. In step (e), impurities are removed from the final mixture to provide substantially pure aqueous arsenic acid.

Claims25

Dependent claims

A process for recovering arsenic acid, H.sub.3 AsO.sub.4, from a starting mixture comprising sulfuric and arsenic acids and water comprising the steps of:

(a) treating a starting mixture, wherein said starting mixture comprises at least about 1 weight percent arsenic acid, H.sub.3 AsO.sub.4, and at least about 1 weight percent sulfuric acid and up to about 98 weight percent water based on the total amount of said starting mixture, with a sulfur (IV) compound which will reduce the arsenic acid, H.sub.3 AsO.sub.4, to an arsenic (III) compound, in order to convert said arsenic acid, H.sub.3 AsO.sub.4, to an arsenic (III) compound and then reacting the arsenic (III) compound with hydrogen fluoride in an amount sufficient to convert the arsenic (III) compound to arsenic trifluoride to thereby produce a resulting mixture which comprises arsenic trifluoride, the sulfur (IV) compound, sulfuric acid, hydrogen fluoride and water;
(b) purging the resulting mixture with a gas which does not oxidize the arsenic trifluoride back to arsenic acid, H.sub.3 AsO.sub.4, in order to remove the sulfur (IV) compound from the resulting mixture to thereby produce a purged mixture which comprises the arsenic trifluoride, sulfuric acid, hydrogen fluoride and water;
(c) separating the arsenic trifluoride from the purged mixture;
(d) reacting the separated arsenic trifluoride from step (c) with an oxidizing agent in order to convert the arsenic trifluoride to arsenic acid, H.sub.3 AsO.sub.4, to thereby produce a final mixture which comprises arsenic acid, H.sub.3 AsO.sub.4, unreacted oxidizing agent, hydrogen fluoride and water;
and
(e) removing impurities from the final mixture, wherein the impurities comprise hydrogen fluoride and unreacted oxidizing agent, to provide substantially pure aqueous arsenic acid, H.sub.3 AsO.sub.4.

3 more elements

A process for recovering arsenic acid, H.sub.3 AsO.sub.4, from a starting mixture comprising sulfuric and arsenic acids and water comprising the steps of:

(a) treating a starting mixture, wherein said starting mixture comprises at least about 1 weight percent arsenic acid, H.sub.3 AsO.sub.4, and at least about 1 weight percent sulfuric acid and up to about 98 weight percent water based on the total amount of said starting mixture, with a sulfur (IV) compound which will reduce the arsenic acid, H.sub.3 AsO.sub.4, to an arsenic (III) compound, in order to convert said arsenic acid, H.sub.3 AsO.sub.4, to an arsenic (III) compound to thereby produce a resulting mixture which comprises the arsenic (III) compound, the sulfur (IV) compound, sulfuric acid, and water;
(b) purging the resulting mixture with a gas which does not oxidize the arsenic (III) compound back to arsenic acid, H.sub.3 AsO.sub.4, in order to remove the sulfur (IV) compound from the resulting mixture to thereby produce a purged mixture which comprises the arsenic (III) compound, sulfuric acid, and water;
(c) treating the purged mixture with hydrogen fluoride in an amount sufficient to convert the arsenic (III) compound to arsenic trifluoride and then separating the arsenic trifluoride from the purged mixture;
(d) reacting separated arsenic trifluoride from step (c) with an oxidizing agent in order to convert the arsenic trifluoride to arsenic acid, H.sub.3 AsO.sub.4, to thereby produce a final mixture which comprises arsenic acid, H.sub.3 AsO.sub.4, unreacted oxidizing agent, hydrogen fluoride and water;
and
(e) removing impurities from the final mixture, wherein the impurities comprise hydrogen fluoride and unreacted oxidizing agent, to provide substantially pure aqueous arsenic acid, H.sub.3 AsO.sub.4.

3 more elements

Dependencies are inferred from the claim text.