Removal of arsenic(III) and arsenic(V) from sulfuric acid solution by liquid–liquid extraction

Abstract

Extraction of arsenic(III) and arsenic(V) from sulfuric acid solution was studied. Cyanex  923, Cyanex  925, dialkyldithiophosphinic acids (Cyanex  301), hydrophobic glycol (2-ethylhexane-1,3-diol), and hydroxamic acids were used as extractants. The efficiency of extraction depended on extractant, diluent, valency of arsenic, and sulfuric acid concentration. Acidic reagents extracted As(III) better than As(V), while the opposite order of extraction efficiency was observed for the solvating extractants. The use of an aromatic diluent (toluene) was preferred. Toluene was found to be a better diluent for the Cyanex  and Cyanex 925 than Exxsol D 220/230 and octane. In the case of neo-decanohydroxamic acids, the type of diluent had no significant effect on extraction of arsenic. The extraction of both As(III) and As(V) increased when the concentration of the sulfuric acid in the feed increased. The co-extraction of sulfuric acid was observed. The extraction with hydroxamic acids was significantly slower in comparison to the extraction with other reagents. Extractant: arsenic species: sulfuric acid molar ratios were determined and they confirmed the composition of extracted species.  2003 Society of Chemical IndustryKeywords: arsenic; Cyanex; hydroxamic acids; polyols; extraction INTRODUCTIONEconomic recovery of As(V) from spent electrorefining sulfuric acid solutions is an important industrial problem. Solvent extraction and ion exchange are used in a few installations.1 -5 In sulfuric acid solutions, As(V) is present in the form of undissociated H 3 AsO 4 . However, in electrowinning processes As(III) species are formed and then, oxidized to As(V). As(III) exists in the form of two hypothetical weak acids: HAsO 2 and H 3 AsO 3 . In strongly acidic solutions As(III) exists in the form of AsO + . Various reagents have been proposed for the recovery of arsenic species.6,7 They include tributyl phosphate and other esters of phosphoric acids, trialkylphosphine oxides, some intermediate derivatives between esters and phosphines, eg R 2 ROP=O, R(RO) 2 P=O,

Treatment of arsenic ions from produced water through hollow fiber supported liquid membrane

“…The acidic reagent, Cyanex ® 301, could extract As(III) better than As(V). Cyanex ® 925 and Cyanex ® 923 were more suitable for As(V) extraction than As(III) [13,[20][21]. The mixture of Cyanex ® 301 with Cyanex ® 925 was good for both As(V) and As(III) [20].…”

“…(7) and (8)), which slowed down and made the stripping difficult [8]. High percentage of extraction by Cyanex ® 301 can be explained from the fact that in a strong acidic solution, arsenic ions (III) are in the form of AsO + that can react with the acidic extractant [20,21].…”

“…9 is a comparative plot of the maximum percentages of the extraction and recovery of arsenic ions from produced water against different extractants. From the results Cyanex ® 923 and TBP offered poor separation performance although the neutral extractants were recommended for the extraction and recovery of arsenic ions [13,[20][21][22][23][24][25]31]. This results agrees that a neutral extractant reacts with only undissociated form (H 3 AsO 3 ) [31] because at the pH of produced water about 6-6.5, arsenic ions exist as H 3 AsO 3 , H 2 AsO 4 − and HAsO 4 2− , as described [29].…”

“…According to Wilson et al [29], it inferred that As(III) in this produced water presented in neutral form or undissociated arsenic of H 3 AsO 3 , and As(V) presented in dissociated arsenics or anion complexes of H 2 AsO 4 − and HAsO 4 2− . It is important to take into consideration that some research groups recommended neutral extractants to extract arsenic in neutral forms [13,[20][21][22][23][24][25]31]. In this regard, the neutral extractants (Cyanex ® 923 and TBP) were used in this work.…”

“…However, because arsenic ions might exist in anion complexes, the basic extractants (TOA and Aliquat 336) were also used. The acidic extractant (Cyanex ® 301) was selected because of its very high efficiency in arsenic extraction as well [20,21]. (1) and (2).…”