Removal of phosphate from water by paper mill sludge biochar
2022
Zhang, Ming | Lin, Kun | Li, Xiaodian | Wu, Lijun | Yu, Jie | Cao, Shuang | Zhang, Dong | Xu, Liheng | Parikh, Sanjai J. | Ok, Yong Sik
Biochar modification by metals and metal oxides is considered a practical approach for enhancing the adsorption capacity of anionic compounds such as phosphate (P). This study obtained paper mill sludge (PMS) biochar (PMSB) via a one-step process by pyrolyzing PMS waste containing ferric salt to remove anionic P from water. The ferric salt in the sludge was transformed into ferric oxide and zero-valent-iron (Fe⁰) in N₂ atmosphere at pyrolysis temperatures ranging from 300 to 800 °C. The maximum adsorption (Qₘ) of the PMSBs for P ranged from 9.75 to 25.19 mg P/g. Adsorption is a spontaneous and endothermic process, which implies chemisorption. PMSB obtained at 800 °C (PMSB800) exhibited the best performance for P removal. Fe⁰ in PMSB800 plays a vital role in P removal via adsorption and coprecipitation, such as forming the ≡Fe–O–P ternary complex. Furthermore, the possible chemical precipitation of P by CaO decomposed from calcite (CaCO₃; an additive of paper production that remains in PMS) may also contribute to the removal of P by PMSB800. Moreover, PMSBs can be easily separated magnetically from water after application and adsorption. This study achieved a waste-to-wealth strategy by turning waste PMS into a metal/metal oxide-embedded biochar with excellent P removal capability and simple magnetic separation properties via a one-step pyrolysis process.
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