Waste controls waste: fluoride adsorption behavior and mechanism on modified phosphogypsum biochar

The use of green methods for the treatment of industrial waste and waste reuse has become a key environmental issue. In order to achieve this goal, this study uses waste phosphogypsum (PG) as raw material to produce adsorbents for wastewater treatment, achieving green reuse of industrial waste. Sodium carbonate (Na₂CO₃) was used to modify PG to explore the safe and rational utilization of PG. The modified phosphogypsum biochar (MP-BC) was prepared by mixing the modified phosphogypsum (MPG) with pineapple peel in proportion and applied to the removal of fluoride from wastewater. The X-ray fluorescence spectrum and X-ray diffraction pattern indicate that the chemical component of MP-BC is mainly calcium oxide, that is, an appropriate amount of modified PG (MPG) can load calcium oxide on biochar, thereby improving the physical properties of biochar. The MP-BC exhibited 133 mg/g maximum fluoride adsorption capacity, and the adsorption rate of fluoride in actual phosphogypsum leachate by MP-BC can reach 97.23%. Furthermore, chemical precipitation was the primary adsorption mechanism. Also, the MP-BC can effectively promote fluoride ion conversion into calcium fluoride. In summary, this study proposes a method of green utilization of PG, which effectively alleviates PG pollution, promotes the reuse of PG, and realizes the “treating waste with waste” of industrial waste.