碳酸化对模拟废物水泥窑共处置产品中重金属浸出的影响

Influence of carbonation on the leaching characteristics of heavy metals in a co-processed cement product

通过模拟煅烧试验制取水泥熟料(重金属以一定的比例掺入水泥生料)并制备混凝土样品,研磨至粒径小于1mm,并使部分样品发生碳酸化作用.并分别对未碳酸化样品和碳酸化样品进行pH静态试验,研究了碳酸化作用对混凝土样品酸中和容量以及重金属(Cr,Ni,As,Cd和Pb)浸出行为的影响.结果表明,未碳酸化样品在碱性范围内(pH=7～12)酸中和容量较大,而碳酸化样品则在弱酸性范围内(pH=5～7)酸中和容量较大;碳酸化作用不影响混凝土中Cr、Ni、Cd、Pb的释放曲线的变化趋势,仅改变了浸出量最小值出现的pH值区间,但是碳酸化作用改变了混凝土中As的吸附相,使其释放曲线发生了明显的改变;碳酸化作用降低了混凝土中Cr、Ni、Cd、Pd的浸出量,但在较大pH范围内(pH=3～7和pH>11),增加了As的浸出量,因此,对混凝土中重金属溶出的安全性评价应重点关注As.

Cement clinker was produced from a cement calcination simulation facility（ heavy metals were mixed into the cement raw meal in a certain proportion） ,and concrete samples were then prepared. The samples were milled to diameters less than 1 mm,some of which were carbonated and others were used as the control group. Tests of the pH-dependence were carried out to study the influence of carbonation on the leaching behavior of heavy metals （ Cr, Ni, As, Cd and Pb） and on the ANC （ acid neutralizing capacity） of cement concrete. Under alkaline conditions （ pH = 7 - 12） the ANC of the non-carbonated samples was larger, however in weak acid conditions （ pH = 5 - 7） the ANC of the carbonated samples was larger. The leaching behavior of heavy metals including Cr, Ni, Cd and Pb was not influenced by carbonation,but the pH of the leaching liquid was changed. The adsorption phase of As was influenced by carbonation and the release rule changed obviously. The amounts of Cr, Ni, Cd and Pb leached from the concrete were reduced after carbonation,but at certain pH （pH = 3 -7and pH 〉 11 ） , the amount of leached As increased. Consequently, the leaching behavior of As should be considered in risk assessment of concrete coproducts.