Microwave‐Assisted Dried Volcanic Tephra/Calcium Alginate Composite for Phosphate Removal from Micro‐Polluted Wastewater

After a kind of volcanic tephra (VT) mineral from Changbai Mountains, Jilin, China, was entrapped into Ca-alginate (CA) beads, dried VT/CA composites were formed by microwave-assisted drying system. The acquired composites were studied for adsorptive removal of phosphate from aqueous solution. The effects of composite dosage (25–250 g/L), initial solution pH (1–10), and initial phosphate concentration (5–50 mg P/L) on phosphate removal were evaluated in a batch mode of operation. Adsorption thermodynamics (changes in the Gibbs free energy, enthalpy, and entropy) and kinetics (adsorption rate constants) have been studied. The results showed that phosphate removal capacity of ca. 0.10 mg P/g composites was achieved for the treatment of micro-polluted wastewater (15 mg P/L) with the dosage of 150 g/L under a shaking rate of 200 rpm. The phosphate removal efficiency was over 90% at aqueous solution pH of 1 to 6. Possible release of elemental ions from VT/CA composites into aqueous solution was analyzed. The mechanism of phosphate removal by the VT/CA composites was discussed and the VT/CA composites were used for phosphate removal from micro-polluted wastewater in rural area in China. Overall, the microwave-assisted dried VT/CA composites had characteristics of being convenient for processing and long-term storage, environmentally friendly, and simple manipulation at small-scale for treatment of micro-polluted wastewater.