磷渣基地聚物材料固化砷钙渣的机理

Solidification/Immobilization of Calcium Arsenate Waste Using Phosphorous Slag Based Geopolymers

以砷含量为7.63%的砷钙渣为研究对象,利用磷渣基地聚物材料对其进行固化处理,并采用毒性浸出实验考察了砷钙渣及固化体砷毒性浸出特性。结果表明:砷钙渣中砷的毒性浸出浓度可达2 450 mg/L,远超过国家毒性浸出鉴别标准限值(5 mg/L)。考察了不同养护时间、不同p H值(1~12)浸取剂环境下固化体中砷的浸出规律。结果表明:在p H=4~8范围内,砷浸出浓度较小;在酸性(p H【4)和碱性(p H】8)条件下砷浸出相对较大,但均小于5 mg/L。并考察了固化体中砷形态变化规律,揭示其固化机理。当养护时间为28 d时,固化体中As(Ⅲ)含量由96.3%降至28.8%,其后随着养护时间的变化固化体中As(Ⅲ)含量呈缓慢降低趋势,180 d As(Ⅲ)含量为12.6%,240 d As(Ⅲ)含量为10.8%。磷渣基地聚物固化砷钙渣机理为:磷渣基地聚物材料水化环境和所含的铁氧化物可使高毒性及强迁移性As(Ⅲ)向相对稳定的As(Ⅴ)转化;随时间的变化,磷渣基地聚物材料不断水化,并提供游离Ca2+、Al3+离子,使砷化合物经沉淀反应生成Al-As-O、Ca-As-O难溶性盐,进而降低砷浸出浓度。

A calcium arsenate waste, containing amounts of arsenic(7.63%), was solidified/immobilized with phosphorous slag based geopolymers. The arsenic leachability of the calcium arsenate waste and the solidified forms was determined via the toxicity characteristic leaching procedure. The results show that the arsenic concentration in the leachate from calcium arsenate waste is 2 450 mg/L, which is greater than the national standard(i.e., 5 mg/L). The effects of curing time and the p H(1 12) value of leaching solution on the arsenic leachability of the solidified samples were investigated. The arsenic concentration of the leachate from the solidified forms is lower when p H =(4-8), and greater when p H<4 and p H>8, which were lower than 5 mg/L. The speciation of arsenic in the solidified samples was analyzed to discover the mechanism for the immobilization of calcium arsenate waste with phosphorous slag based geopolymers. The As(Ⅲ) content in the solidified sample firstly decreases from 96.3% to 28.8% after the curing time of 28 d, and then slowly decreases for the prolonged curing time. The As(Ⅲ) content decreases to 12.6% and 10.8% for 180 d and 240 d curing, respectively. It is indicated that the mechanism for the immobilization of calcium arsenate waste with phosphorous slag based geopolymers can be generally attributed to two aspects, i.e., the As(Ⅲ) with a high toxicity and a strong mobility is oxidized to the relatively stable As(Ⅴ) in the treated samples by the iron oxides in the phosphorous slag during the hydration of phosphorous slag based geopolymers, and the phosphorous slag based geopolymers are continuously hydrated for the prolonged curing time. A great amount of free Ca2+ and Al3+ ions are provided to promote the formation of sparingly soluble Al As O and Ca As O compounds, thus decreasing the arsenic leachability of the solidified sample.