三价铁离子浓度对As(V)-Fe(II)-Fe(III)体系沉淀臭葱石的影响

在常压、95℃、初始pH=1.5的条件下，研究了As(V)–Fe(II)–Fe(III)体系中初始Fe(III)浓度对砷的去除率和臭葱石合成的影响。结果表明，溶液中初始Fe(III)/As(V)摩尔比为0时，沉淀产物为结晶度良好的臭葱石，但砷的去除率仅为24.3%，沉淀浸出砷浓度高于国标规定的浓度限值5 mg/L。溶液中初始Fe(III)/As(V)摩尔比大于0时，在升温过程中生成了无定形砷酸铁，当初始Fe(III)/As(V)摩尔比不超过1.6时，砷酸铁反应8 h后转化为臭葱石；随初始Fe(III)/As(V)摩尔比增大，砷的去除率增大，臭葱石沉淀的结晶度降低、浸出砷浓度降低；其中，初始Fe(III)/As(V)摩尔比为0.8和1.6时，臭葱石沉淀的浸出砷浓度低于5 mg/L，适合安全堆存。当初始Fe(III)/As(V)摩尔比大于1.6时，无定形砷酸铁反应8 h仍不能转化成臭葱石，砷的去除率降低，沉淀浸出砷浓度超标，不适合安全堆存。

Effect of ferric ion concentration on atmospheric scorodite synthesis in As(Ⅴ)-Fe(Ⅱ)-Fe(Ⅲ) system

The present study is focused on the synthesis of scorodite (FeAsO4?2H2O) at 95℃ and initial pH 1.5 under atmospheric pressure. In particular, the effects of initial ferric ion concentration of the solution on the arsenic removal rate and the scorodite formation were investigated in As(V)?Fe(II)?Fe(III) system. The experimental results showed that the well crystalline scorodite was formed through oxidizing ferrous ions by air stream when there was no additional ferric ion in the solution, but only 24.3% of arsenic could be removed and the United States Environmental Protection Agency's Toxicity Characteristic Leaching Procedure tests showed that the arsenic leaching concentration of scorodite was more than 5 mg/L, higher than the arsenic concentration limit set by the national standard. In all the experiments with the additional ferric ions, it was found that there was amorphous ferric arsenate formed in the heating process. The amorphous ferric arsenate was found to converted to crystalline scorodite in 8 h if the initial Fe(III)/As(V) molar ratio was not higher than 1.6. However, the crystallinity of scorodite decreased with the increase of additional ferric ion concentration, the arsenic leaching concentration of solid products decreased and the arsenic removal rate of the solution were improved. The results of the TCLP leaching test showed that at the initial Fe(III)/As(V) molar ratio of 0.8 and 1.6, the arsenic leaching concentration of the formed solid products were less than 5 mg/L, which could meet the emission standards, so that the solid products may be considered to be stable for safe disposal. Nevertheless, if the initial Fe(III)/As(V) molar ratio was higher than 1.6, the amorphous ferric arsenate could not convert to crystalline scorodite after 8 h. The arsenic removal rate decreased and the amorphous ferric arsenate was unstable for high arsenic leaching concentration. Experimental results suggested that adding appropriate ferric in solution containing arsenic and ferrous could contribute to forming stable scorodite and promoting arsenic precipitation.