An innovative method for synergistic stabilization/solidification of Mn2+, NH4+-N, PO43- and F- in electrolytic manganese residue and phosphogypsum.

Electrolytic manganese residue (EMR) contains large quantities of manganese (Mn2+) and ammonia nitrogen (NH4+-N). Phosphogypsum (PG) contains plenty of phosphate (PO43-), fluorine (F-) and some heavy metals. Separate storage of EMR and PG could seriously damage the ecological environment. In this study, synergistic stabilization/solidification (S/S) of EMR and PG was studied. The effects of EMR:PG mass ratio, S/S pH, solid-liquid ratio and temperature on the concentrations of NH4+-N, PO43-, Mn2+ and F- in the leaching solution, and the characteristics of EMR and PG were studied. Meanwhile, the synergistic S/S mechanisms of EMR and PG, and leaching test were investigated. The results showed that the concentrations of F-, PO43-, NH4+-N and Mn2+ in the leaching solution were 4.5 mg/L, 13.6 mg/L, 55.5 mg/L and 0.8 mg/L, respectively, when the mass ratio of EMR to PG was 1:2 and the pH was 9.0 adjusted by MgO after 20 days S/S. Manganese was mainly solidified as Mn3(PO4)2·7H2O and Mn(OH)2, and ammonia nitrogen was mainly stabilized as struvite; fluorine was mainly stabilized as (Mn, Ca, Mg)F2, and phosphate was mainly solidified as (Mn, Ca, Mg)3(PO4)2 and (Mn, Ca, Mg)HPO4. The leaching test results showed that PO43- and NH4+-N were reduced to 13.6 mg/L and 55.5 mg/L, respectively, and the concentrations of all the measured heavy metals and F- were within the permitted level for the GB8978-1996 after 20 days S/S.