Abstract: In an attempt to evaluate the potential of using magnesite slag as a solid magnesium source for the recovery of phosphorus in constructed wetland, we investigated the characteristics and influencing factors of magnesium extraction from magnesite slag by HCl leaching. Results revealed that when the particle size of magnesite slag was less than 150 μm and the particle concentration was 5 g/L, the concentration of magnesium ion in leaching solution increased gradually with the prolongation of leaching time until equilibrium was reached five hours later. With the decline of hydrochloric acid concentration in the leaching solution, the concentration of magnesium ion decreased correspondingly. However, when magnesite slag (particle size < 150 μm) was soaked in hydrochloric acid solution (concentration 1 mol/L) for five hours, increasing the magnesite slag concentration would reduce the extraction efficiency. The extraction of magnesium reached maximum (117.70 mg/kg) when hydrochloric acid concentration was 1 mol/L and magnesite slag concentration was 5 g/L. Under such optimal extraction condition, the extracted magnesium was almost acid soluble, accounting for 92% of the total extracted amount. After leaching, magnesite slag’s ability of adsorbing phosphorus in solution was improved as the mineral lattice was destroyed, and the particle size of magnesium slag decreased while the specific surface area increased. In theoretical sense, the magnesium ions in the leaching solution could recover 810 mg phosphorus per kilogram of magnesium slag, indicating that magnesite slag has good potential in phosphorus recovery.

Key words: magnesium mineral residue, magnesium ion, HCl soaking, phosphorus recovery, release kinetics, constructed wetland