Adsorption Properties And Mechanism Of Pb²⁺ By Acid Modified Sludge/phosphogypsum Ceramsite

The sludge/phosphogypsum ceramsite was prepared from solid waste,such as municipal sludge,phosphogypsum and red mud.The basic properties of ceramsite,such as bulk density,mud content and hydrochloric acid solubility,were measured.The adsorption of Pb²⁺by ceramsite was studied,and the ceramsite with the best adsorption performance was determined.A series of hydrochloric acid modified ceramsite?HC?,nitric acid modified ceramsite?NC?and citric acid modified ceramsite?CC?were obtained by modifying the ceramsite with different concentrations of HCl,HNO₃ and C₆H₈�H₂O.The adsorption effect and mechanism of Pb²⁺on the modified ceramsite were studied.Combined with Boehm titration,pHpzc,FTIR and specific surface area,the adsorption mechanism of Pb²⁺on ceramsite surface was analyzed.Through static test,the effects of adsorption reaction time,initial concentration of Pb^2+,pH value of solution,dosage of ceramsite,and temperature of reaction system on the removal of Pb²⁺from water by modified ceramsite were studied,the best experimental conditions were determined,and the adsorption isotherm model and adsorption kinetics model were used for linear fitting analysis.The conclusion is as follows:?1?The ceramsite made of sludge,phosphogypsum and red mud at the mass ratio of 5:3:2 and calcination temperature of 950?showed the best adsorption.And the adsorption rate of Pb²⁺was 99.99%,and the adsorption capacity was 4.9995mg/g.?2?When the acid concentration was 1mol/L,the adsorption rate of Pb²⁺by HC and NC reached the maximum,90.38%and 88.57%respectively.When the acid concentration was 0.5mol/L,the adsorption rate of Pb²⁺by CC reached the maximum?57.85%?which was lower than that of unmodified ceramsite?66.86%?.?3?Compared with unmodified ceramsite,the content of acid groups on the surface of modified ceramsite increased?except for 5 mol/L citric acid?,and the acid groups of HC,NC and CC increased by 72%,75%and 69%,respectively.After Pb²⁺adsorption,the acid group content of all ceramsites decreased,especially the content of carboxyl and hydroxyl groups,indicating that a large number of carboxyl and hydroxyl groups participated in the adsorption of Pb²⁺.?4?After modification,the pHpzc value of ceramsite was significantly lower than that before modification.The pH value of Pb²⁺solution was 5.When pH=5,lead mainly exists in the form of Pb²⁺,Pb?OH?⁺,Pb?OH?₂?aq?and Pb?OH?₂?s?.When pH<pHpzc value,ceramsite still has the adsorption effect on the solution containing lead.?5?FTIR and BET analysis showed that-OH,C-O and other groups participated in the adsorption process of Pb²⁺.The structure of the modified ceramsite was porous,with large specific surface area and developed pores,which was conducive to the adsorption.The adsorption of Pb²⁺by modified ceramsite has surface adsorption.?6?The adsorption properties of HC to Pb²⁺can be described by Langmuir equation,the adsorption properties of NC and CC to Pb²⁺can be described by Freundlich equation,and the three modified ceramsites show single molecular layer adsorption,and the adsorption reaction to Pb²⁺conforms to the quasi second-order reaction kinetics equation.?7?The initial pH value and adsorption time of the solution were positively correlated with the removal rate of Pb²⁺,while the amount of adsorbent and initial concentration of the solution were negatively correlated with the removal rate.The temperature had little effect on the adsorption of Pb²⁺on all samples.The optimal initial pH value of the solution was 5,the initial concentration of the solution was 200mg/L,the dosage of adsorbent was 2g/L,the adsorption time was 1h?HC and NC?and 2h?CC?,and the adsorption temperature was 25?.?8?According to Langmuir equation parameters,NC has better adsorption performance for Pb²⁺,and the binding force of Pb²⁺and HC is the strongest.