Mechanochemical Activation of Antigorite to Provide Magnesium and Hydroxide Ions for Recovering Phosphorus and Nitrogen from Wastewater as Struvite

Abstract

Phosphorus (P) and nitrogen (N) can be simultaneously recovered by struvite (MgNH4PO4·6H2O) crystallization, and this has attracted more and more attention. However, the cost of producing struvite from wastewater is high due to the chemical inputs, which makes the struvite process unattractive in terms of economic benefits. Thus, it is important to develop a new struvite technology with low cost and simple operation. In this work, the antigorite was activated by a ball-milling process. The crystal form of the antigorite was destroyed by the mechanical forces, leading an increase in the dissolution of Mg2+ and OH− in the structure. The concentration of Mg2+ dissolved into water increases with the milling time, as well as the pH. Additionally, the dissolution of the activated antigorite depends on the concentration of phosphate-ammonium. The responsive dissolution makes the activated antigorite adaptively adjust the dissolution of Mg2+ and OH− and maintain a stable recovery of nitrogen and phosphorus from wastewater. The performance of P and N recovery was investigated by moderating variables, including the molar ratio of N/P, activation time, reaction time, and dosage. The results showed that the activated antigorite in the wastewater can be automatically converted into struvite. Actual swine wastewater was treated by the activated antigorite process, and a recovery rate of 98% was achieved by adding 1.2 g/L activated antigorite. The economic evaluation shows that the cost of the activated antigorite process is only 36% of an ordinary chemical process (MgSO4 and NaOH).