Characteristic of geopolymer modified by MgO and its adsorption capacity of phosphate and ammonium ions from swine wastewater

Discharges of nitrogen and phosphorus from wastewater continue to be a widespread environmental problem causing eutrophication and harm to aquatic environments. In this study, the NH4+-N and PO43--P adsorption capacity of a casting dust-based polymer (FDG) synthesized from casting dust (FD), and a FDG modified by MgO to obtain magnesium modified geopolymer (MFDG), were investigated. FDG was found to have almost zero capacity to adsorb PO43--P, while adsorption of NH4+-N and PO43--P by MFDG fitted well with the Langmuir model and the pseudo-second-order kinetic model. The maximum adsorption capacity of NH4+-N and PO43--P by MFDG was 230.69 mg/g and 175.09 mg/g, and its adsorption capacity of NH4+-N was 18.3 times higher than that of FDG. pH 9 was found to be optimal for adsorption of NH4+-N and PO43--P by MFDG and the NH4+-N and PO43--P reaction with Mg2+ to form struvite is the main process. Penetration times for NH4+-N and PO43--P were about 200 h and 40 h when an adsorption column filled with MFDG was used to purify swine wastewater with flow rate of 2 mL/min. These results demonstrated that MFDG is a good absorbent, and could have an important application in treatment of wastewater.