Effect of thermal treatment coupled with acid activation on phosphate adsorption by alum sludge
Alum sludge(AIS)originating from water treatment plants possesses notable phosphate adsorption and chelating capabilities,due to its rich content of aluminum and iron oxides.However,the effectiveness of AIS in phosphate adsorption is often hampered by its complex composition and the presence of impurities.To overcome these obstacles,this study adopted a simple yet effective method that combines thermal treatment with acid activation.The results showed that after being subjected to thermal treatment at 600℃ for lhour and then activated with 2.0mol/L hydrochloric acid at a solid-liquid ratio of 1∶1,the AIS achieved a phosphate adsorption capacity of 18.3mg/g.This represented a 2.4-fold increase compared to the untreated AIS.Furthermore,the treated AIS demonstrated remarkable stability in tests involving the coexistence of anions and cations,as well as metal ion dissolution.The investigation into adsorption kinetics and thermodynamics revealed that the adsorption process was primarily driven by chemisorption.Complementary analyses using SEM,XRD,and BET further confirmed that the adsorption mechanism was dominated by ligand exchange.Additionally,electrostatic attraction,hydrogen bonding,and surface deposition also played pivotal roles in the adsorption process.These findings not only provide a promising perspective on alum sludge disposal and phosphorus pollution control but also embody a promising win-win strategy of"turning waste into treasure".
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