全烧垃圾流化床炉飞灰制备免烧砖的性能研究

开展了水泥固化全烧垃圾循环流化床焚烧炉飞灰特性及其制备免烧砖的研究.同时,分析了飞灰的特性,研究了水泥用量对砖体抗压强度和重金属浸出毒性的影响,并对固化前后飞灰在不同p H值溶液环境下的重金属渗滤特性和基于改进RCR连续提取法的重金属形态分布进行了对比研究.结果表明:飞灰中Cd、Cu、Pb、Ni的浸出浓度分别达到1.76、60.29、5.36、1.48 mg·L-1,远超出生活垃圾填埋标准的规定,Cd、Zn、Cu的酸可交换态部分很高,分别为48%、21.26%、20.72%.水泥基材具有良好的稳定效果,添加量达到30%时,免烧砖中重金属的浸出毒性已远低于标准值.随着水泥掺量的提高,免烧砖的抗压强度呈上升趋势,当水泥比例为30%时,强度可达到12.8 MPa,35%水泥比例的砖体,其抗压强度则达到国标建筑用砖的MU15级.与原始飞灰相比,砖体中重金属在不同渗滤液p H下的浸出趋势并未改变,浸出量却显著下降,p H的适应范围变宽.另外,重金属中酸可交换态部分降至低于1%,主要转变成了可还原态,对环境的污染风险大幅降低.

Performance of non-fired brick making from fly ash in a purely burning municipal solid waste circulating fluidized bed incinerator

The stabilization/solidification of fly ash, generated from a purely burning municipal solid waste (MSW) circulating fluidized bed incinerator, and the performance of solidified fly ash making non-fired brick are investigated in the present work. The characteristic of the raw fly ash is analyzed, and the effects of cement addition on compressive strength of the brick and leaching toxicity of heavy metals are discussed in this paper. For heavy metals in fly ashes before and after solidification, pH-dependent leaching behavior and speciation distribution on basis of optimized BCR sequential extraction procedure of heavy metals are compared. Results show that the leachate of raw fly ash contains high concentration of Cd (1.76 mg·L^-1), Cu (60.29 mg·L^-1), Pb (5.36 mg·L^-1) and Ni (1.48 mg·L^-1), which are far beyond the limit of Chinese sanitary disposal limitation. The acid extractable/exchangeable fraction of Cd, Zn and Cu reach 48%, 21.26% and 20.72%, respectively. Cement exhibits sound efficiency in immobilizing the heavy metals in fly ash. The non-fired bricks mixed by 30% cement could reduce heavy metal leaching toxicity far below the limitation. The compressive strength of the matrix improves as the increasing mixing percentage of cement. The compressive strength is 12.8 MPa for 30% cement mixing and meets the requirement of MU15 class in Chinese national standard for building bricks when 35% cement mixing is applied. Compared with the raw fly ash, leaching trend of heavy metals in solidified matrix in different pH value leachates does not change, but the leaching concentrations remarkably decline and the safe pH value region becomes even wider. The acid extractable/exchangeable fraction of heavy metals in solidified matrix with 30% cement reduces below 1%, which is mainly the easily reducible fraction and significantly decreases the pollution risk.