富含钙/铝的污泥生物炭复合材料对水溶液中磷酸盐的吸附机制

Adsorption Mechanism for Phosphate in Aqueous Solutions of Calcium/Aluminum-rich Sludge Biochar Composite

剩余污泥富含有机物,同时也含有重金属和病原体等有害物质.以水铝钙石和剩余污泥为原料,通过共混凝和共热解技术制备生物炭以降低污泥中重金属溶出风险,并对其磷酸盐吸附性能开展研究.结果表明,污泥生物炭中的Zn、Cu、Cd和Ni浸出量随水铝钙石投加量的增加而减少.水铝钙石与剩余污泥质量比为1∶1时,共热解制备得到的富含钙/铝污泥生物炭复合材料(1∶1HB800)重金属浸出风险最低,并对磷酸盐表现出较高的吸附能力,其过程可用Langmuir吸附等温线(R2=0.93)拟合,在25℃条件下对磷的最大吸附容量为51.38 mg·g^(-1).1∶1HB800对高浓度磷的吸附过程符合拟二阶动力学模型,吸附速率由表面吸附和颗粒内扩散共同控制.相较于中性溶液,1∶1HB800对酸性和碱性水溶液中的磷酸盐具有更好的去除效果,这与1∶1HB800中钙/铝在不同pH条件下的浸出量及铝元素的存在形式有关.FTIR、XRD、SEM、零点电位和钙/铝离子的浸出实验分析结果表明,1∶1HB800对磷的吸附机制主要是共沉淀(Ca^(2+)/Al^(3+)与磷相互作用),配体交换(羟基)和静电相互作用.因此,1∶1HB800为去除水溶液中的磷提供了一种可行的替代选择,也为剩余污泥资源化和无害化处理提供了一种潜在的新方法.

Excess sludge is rich in organic matter but also contains heavy metals,pathogens,and harmful substances.In this study,hydroaluminite and excess sludge were used as raw materials to reduce the risk of heavy metals leaching from sludge by coagulation and co-pyrolysis,and its phosphate adsorption characteristics were studied.The results showed that the leaching amount of Zn,Cu,Cd,and Ni in sludge biochar decreased with the increase in the hydroaluminite dosage.The sludge biochar composite(1∶1HB800),prepared by co-pyrolysis of hydroaluminite and excess sludge with a mass ratio of 1∶1 as well as rich in calcium and aluminum,had lowest leaching risk of heavy metals and showed the high adsorption capacity for phosphate.The process could be fitted by the Langmuir adsorption isotherm(R2=0.93),and the maximum phosphate adsorption capacity at 25℃was 51.38 mg·g^(-1).The pseudo second-order kinetic model could well describe the adsorption process of 1∶1HB800 for high concentration phosphate,and its adsorption rate was controlled by both surface adsorption and particle diffusion.Compared with that in the neutral solution,1∶1HB800 had better phosphate capacity in the acidic and alkaline aqueous solutions,which was related to the leaching amount of calcium/aluminum in 1∶1HB800 and the existence form of aluminum under the different pH conditions.FTIR,XRD,SEM,zero potential point,and Ca^(2+)/Al^(3+)leaching experiments indicated that the main adsorption mechanisms for phosphate by 1∶1HB800 were co-precipitation(interaction between Ca^(2+)/Al^(3+)and phosphate),ligand exchange(hydroxyl),and electrostatic interaction.Therefore,1∶1HB800 can provide a feasible alternative for the removal of phosphate in aqueous solutions and also provide a potential new method for the resource utilization and harmless treatment of excess sludge.