Sorption Behavior of Phosphate on an MSWI Bottom Slag and Sewage Sludge Co-sintered Adsorbent

Abstract

Bottom slag and sewage sludge discharged from municipal solid waste incineration and sewage treatment plants were co-sintered for use as a cost-effective adsorbent for phosphate removal from aqueous solutions. The Langmuir isotherm model (which gives a better description of phosphate sorption than the Freundlich model) was adopted to describe the action of the synthesized adsorbent and also for phosphate sorption by either zeolite or ironstone. The model showed that the maximum sorption capacity of the synthesized adsorbent (27,030 mg kg–1) was 38.2 greater than for zeolite and 70.6 times greater than for ironstone. Desorption of phosphate from the synthesized adsorbent at different initial concentrations was about 4.98 %, which was several times lower than for zeolite. The phosphate removal capacity of the synthesized adsorbent remained constant for solution pH values ranging from 3 to 10, which was an improvement on the capacity of the other two adsorbents; its buffering capacity was also superior. The immobilization of phosphate on the synthesized adsorbent might be attributed mainly to complexation with Fe, Al, and Ca ions. Heavy metal ion concentrations in the leachate of the synthesized adsorbent were negligible.