[Chemical extraction of arsenic co-precipitated with amorphous Fe (OH)3 and Fe3O4].

The mobility and bioavailability of As combining with amorphous Fe oxides is vulnerable to the environment.In order to figure out the specific effects of ageing time,Fe/As molar ratio and extractant-to-solid ratio on As extraction procedure,we chose 1 mol·L-1 hydrochloride acid and 0.2 mol·L-1 ammonium oxalate/oxalic acid as extractants to extract synthetic Fe(OH)3-As and Fe3O4-As co-precipitates.The results showed that: ① During the extraction of Fe(OH)3-As and Fe3O4-As co-precipitates by 1 mol·L-1 hydrochloride acid,extractant-to-solid ratio should be 50 and 200,respectively;while extracted by 0.2 mol·L-1 ammonium oxalate/oxalic acid,the molar ratio of C2O2-4 to Fe in Fe(OH)3 and Fe3O4 solid phases should be 4 and 2.5,② The extraction time conducted by hydrochloride acid and ammonium oxalate/oxalic acid should be within 2 hours.③ The Fe-to-As molar ratio and ageing at room temperature had a little influence on the extraction of Fe(OH)3-As co-precipitation,but significantly influenced on Fe3O4-As co-precipitation.With increase of the Fe/As molar ratio and extension of the ageing time,the Fe3O4-As co-precipitate became more difficult to be dissolved.④ It was worth noting that,As would be re-adsorpted by the insoluble solid phase during the extraction by hydrochloride acid and ammonium oxalate/oxalic acid.So the inaccurate measurement would emerge during the extraction of As combining with amorphous Fe oxides.