含砷石膏渣水泥固化/稳定化:预煅烧影响和砷固化机理（英文）

Solidification/stabilization of arsenic-bearing gypsum sludge using Portland cement: precalcination effect and arsenic immobilization mechanism

提出了一种预煅烧和水泥固化/稳定化相结合的无害化处置含砷石膏渣方法,研究了预煅烧影响及砷固化机理.含砷石膏渣中砷含量为8.56%,浸出毒性高达1097.5 mg/L,远高于《危险废物鉴别标准GB5085.3-2007》中危废鉴别值5 mg/L.预煅烧温度为600和700℃时,石膏渣中亚砷酸盐分解导致总砷量和砷迁移性降低,砷浸出毒性可显著降低至较低水平（41.2和4.2mg/L）.采用水泥固化可降低砷浸出毒性和控制砷泄露风险,较高温度（600和700℃）预煅烧后的石膏渣经水泥固化后抗压强度分别达4.2和5.2 MPa,砷浸出毒性分别达到0.98和0.22 mg/L,低于GB5085.3-2007危废限值.砷以Ca2As2O7和AlAsO4形式被包裹或吸附在C-S-H水化产物中,降低了砷迁移性;预煅烧可加速石膏渣水泥固化中砷参与水泥水化和化合反应,导致更多且密实的AlAsO4和Ca2As2O7相形成,强化砷固化效果.该方法有利于含砷量高和毒性高的含砷石膏渣处置,固化体可直接进入垃圾填埋场.

Arsenic-bearing gypsum sludge（ABG sludge）, designated as one of the most important hazardous waste with high arsenic leaching toxicity in the metallurgical industry of nonferrous heavy metals, was treated by a hybrid technology combined with processes of precalcination and solidification/stabilization（S/S） using Portland cement for the arsenic immobilization. The precalcination effect and mechanism of arsenic immobilization were investigated in the S/S process. ABG sludge had an arsenic content of 8.56%, and its arsenic leaching concentration is high up to 1097.5 mg/L. The solidified fresh sludge had a high arsenic leaching concentration and low compression strength with a poor stability in acid neutralization capacity test. Those result indicated a further intensification of arsenic stablization was needed for the fresh sludge. Precalcination could reduce the arsenic leaching concentrations of sludge to a low level（41.2 and 4.2 mg/L for 600 and 700℃） when temperatures equal to or greater than 600℃ due to the removal of As（III）. In subsequent S/S process, encapsulation and adsorption of arsenic in form of Ca2As2O7 and AlAsO4 by C-S-H products were responsible for the immobilization of arsenic in cement-sludge pastes. Precalcination also promoted the interaction between cement and arsenic in pastes, resulting in the intensification of AlAsO4 and dense Ca2As2O7 phase. The solidified pastes of ABG sludge precalcined at 600 and 700℃ possessed arsenic leaching concentrations（0.98 and 0.22 mg/L） lower than that of limit value（5 mg/L in GB5085.3-2007）. This technology showed a favorable performance for the immobilization of ABG sludge and the solidified pastes are feasible for landfill disposal.