Alum sludge-derived zeolite A for the adsorption of typical pollutants in urban non-point source pollution

The management of alum sludge in waterworks has received a large amounts of attention. Considering its high aluminum and silicon content, alum sludge holds great potential as a low-cost raw material for zeolite synthesis to decrease the waste disposal. Alum sludge was utilized to synthesize zeolite A via both fusion-hydrothermal (Fusion-HT) and conventional hydrothermal methods. The synthesis parameters were explored including the Si/Al ratio, the calcination temperature, NaOH amounts, and hydrothermal temperature and time. The zeolite A prepared with Fusion-HT method exhibited a relative crystallinity of 93.15 % and a specific surface area of 128.01 m 2 /g. In adsorption experiments, zeolite A demonstrated excellent maximum adsorption capacities according to the Langmuir model for Cd 2+ , Cu 2+ , NH 4 + , and PO 4 3- , reaching 103.324, 93.899, 38.461, and 6.062 mg/g, respectively. Influential factors such as adsorbent dosage, pH, and humic acid (HA) were investigated. Zeolite A revealed optimal adsorption pH for various ions: Cu 2+ and Cd 2+ exhibited maximum removal efficiencies at pH 3–7, NH 4 + achieved peak adsorption capacity at pH 4–7, and PO 4 3- showed the highest adsorption efficacy at pH 4–6. Besides, the removal trends of Cd 2+ , NH 4 + , and PO 4 3- were negatively correlated with the HA concentration, while the removal rates of Cu 2+ increased first and then decreased. The different removal mechanisms were identified for Cd 2+ , Cu 2+ , NH 4 + , and PO 4 3- . Additionally, zeolite A could be regenerated with over 90 % of Cd 2+ removal efficiency after five cycles, highlighting its great potential in the treatment of urban non-point source pollution.