Influence of Synthesis Temperature on Phosphate Adsorption by Zn-Al Layered Double Hydroxides in Excess Sludge Liquor

A group of Zn-Al layered double hydroxides（LDHs）were synthesized at different temperatures from 25–90°C in order to investigate the influence of synthesis temperature on characteristics of the LDHs and their phosphate adsorption behaviour.The results reveal that an increase in the synthesis temperature generally improves the specific surface area of the sample and the phosphate adsorption capacity.The significantly enhanced crystallinity of the Zn-Al-30,synthesized at 30°C,leads to a remarkable decrease in the specific surface area and conse- quently a poor phosphate adsorption capacity.It is suggested that the surface adsorption plays an important role in the phosphate uptake by the Zn-Al LDHs.Zn-Al-70 presents a relatively higher crystallinity and a lower specific surface area,compared with Zn-Al-60 and Zn-Al-80,but the highest phosphate adsorption capacity,indicating that surface adsorption is only one of the pathways for phosphate removal.The phosphate adsorption by the Zn-Al follows a pseudo-second-order kinetic equation.The adsorption isotherms fit Langmuir models,and the maximum adsorption capacities of the Zn-Al-25,Zn-Al-50 and Zn-Al-70 are estimated to be 17.82,21.01 and 27.10 mg·g -1 adsorbent,respectively.