NH_4^+对次生铁矿物形成及重金属去除的影响

Effect of NH_4^+ on the formation of secondary iron minerals and the removal of heavy metals

研究了初始p H值、Fe^(2+)浓度、Fe/NH_4^+物质的量比对嗜酸性氧化亚铁硫杆菌(A.ferrooxidans)体系中Fe^(2+)氧化率、总Fe沉淀率、次生铁矿物矿相的影响,并比较矿物对AMD中Cr(Ⅵ)、As(Ⅲ)的去除效果.结果表明,当NH_4^+浓度在A.ferrooxidans耐受范围内时,Fe^(2+)氧化及总Fe沉淀去除效果不受影响,表现在160,80,20mmol/L的Fe^(2+)分别在72,48,24h内被完全氧化,培养至终点时(96h)平均总Fe沉淀率分别为24.03%,19.46%,8.13%.在Fe^(2+)=160mmol/L体系中,Fe/NH_4^+=2.0、p H=2.6处理获得纯净施氏矿物;而当Fe/NH_4^+≤1.0、p H≤2.3时,次生铁矿物的合成途径开始向黄铵铁矾转移.Fe/NH_4^+=2.0的各酸性体系合成矿物对Cr(Ⅵ)、As(Ⅲ)去除能力存在显著差异,依次为p H=2.6>p H=2.3>p H=2.0.分析表明,次生铁矿物的表观结构和比表面积是影响有毒元素去除效果的主要原因.

In this study,the influence of initial p H,Fe2＋concentration,molar ratio of Fe/NH4＋on the Fe2＋bio-oxidation rate,total Fe deposition efficiency,and phases of secondary iron minerals in simulated AMD containing A.ferrooxidans was investigated.The Cr（Ⅵ）and As（Ⅲ）removal efficiency of different iron minerals were compared.The results indicated that under the concentration of NH4＋was lower than that for A.ferrooxidans tolerance value,Fe2＋oxidation and total Fe removal through precipitation were not affected,160,80,and 20mmol/L of Fe2＋could be completely oxidized by A.ferrooxidans within 72,48,and 24h,and the average total Fe removal efficiency was 24.03%,19.46%,and 8.13%at the end of the experiment（96h）,respectively.In addition,in initial 160mmol/L Fe2＋system,when the molar ratio of Fe/NH4＋=2.0 and p H=2.6,the secondary iron mineral obtained was pure schwertmannite;when the molar ratio of Fe/NH4＋≤1.0 and p H≤2.3,ammonium jarosite began to occur in this system.Additionally,the Cr（Ⅵ）and As（Ⅲ）removal efficiency of secondary iron minerals harvested from the Fe/NH4＋=2.0systems differed（p H=2.6〉p H=2.3〉p H=2.0）.The data obtained from this study demostrated that the removal efficiency of toxic elements was mainly influenced by the apparent structure and specific surface area of secondary iron minerals.