无定形Fe (OH)3 和Fe3 O4 共沉淀态As的化学提取

无定形铁氧化物结合态砷的迁移性和生物可利用性易受环境变化影响.分别以1 mol·L-1盐酸和0.2 mol·L-1草酸铵缓冲溶液为提取剂,以新制备和室温老化(3个月、6个月)的共沉淀态Fe(OH)3-As和Fe3O4-As为提取对象,研究提取时间、液固比、Fe/As摩尔比和室温老化对As提取效率的影响.结果表明,1 mol·L-1盐酸提取Fe(OH)3-As、Fe3O4-As共沉淀时液固比应分别为50、200左右,0.2 mol·L-1草酸铵缓冲溶液提取Fe(OH)3-As、Fe3O4-As共沉淀时需保证加入的草酸根与固相中Fe的摩尔比分别为4、2.5;盐酸和草酸铵缓冲溶液提取时间2 h即可.样品Fe/As摩尔比和室温老化对Fe(OH)3-As共沉淀的溶解提取影响不大,但对Fe3O4-As共沉淀的提取影响比较大,Fe/As摩尔比越大,Fe3O4-As共沉淀越不易被提取;老化时间越长,其中共沉淀的As越不易被溶解提取.值得注意的是:盐酸和草酸铵缓冲溶液提取过程中如果有不溶固相存在,会发生As的再吸附,使无定形铁氧化物共沉淀态砷的测定不准确.

Chemical Extraction of Arsenic Co-precipitated with Amorphous Fe (OH) 3 and Fe3 O4

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 C₂O₄^2- 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.