高钙高铁煤渣处置含砷污酸的除砷行为及机理

Behaviour and Mechanism of Arsenic Removal From High-arsenic Waste Acid Using Ca/Fe-enriched Coal Slag

针对重有色冶炼过程中的污酸处置长期存在危废产量大、环境成本高等难题,本文提出一种绿色工艺,结合高铁高钙煤渣特征,提出了高铁高钙煤渣无害化处置含砷污酸的新思路,达到去除污酸中砷离子且生成稳定含砷化合物的目的。研究了污酸与高铁高钙煤渣的在不同条件(加入量、反应时间、初始pH)的反应行为,并借助材料分析手段揭示了除砷机理。结果表明燃煤渣富含钙和铁氧化物,煤渣与污酸具有良好的反应效果和除砷作用。燃煤渣用于污酸除砷,最高除砷率可达98.31%,除砷能力最高可达82.52 mg/g,随着反应时间增加除砷效率和沉淀物稳定性明显提高。初始pH=0.98时,除砷效果最好,并且随着pH升高显著下降。煤渣中氧化铁溶于污酸,释放Fe3+,在氧化条件下沉淀砷酸根离子生成无定形砷酸铁,而后在Si、Al和Ca氧化物保护下,达到除砷固砷目的,形成浸出毒性低于5 mg/L的富砷沉淀渣。

The smelting industries of nonferrous metals are suffering from the emission of large number of hazardous wastes and high cost of environmental protection during the disposal of waste acid.We proposed to remove arsenic from waste acid using Ca/Fe-enriched coal slag to produce arsenic-stabilized precipitates.In combination with materials’characterization,the reaction behaviors(dosage of coal slag,reaction time and initial pH)between coal slag and waste acid have been investigated,and the reaction mechanism was also explored.The results shows that coal slag mainly composes of Ca and Fe oxides and exhibits high activity for arsenic removal from waste acid.At a coal slag-to-waste acid ratio of 100 g/L,the arsenic concentration decreases from 7 g/L to 118.2 mg/L and its arsenic removal capacity reaches 68.82 mg/g.The stability of arsenic-enriched precipitates increases with the increasing reaction time.Highest arsenic removal efficiency was obtained at an initial pH of 0.98 and it deceases with the increasing pHs.It is found that Fe oxides in coal slag dissolve in waste acid and then Fe3+precipitates arsenate to form ferric arsenate.Under the protection of Si,Al and Ca oxides,the ferric arsenate is fixed in precipitates and results a lower arsenic leaching concentration in leaching testes.