Extraction of phosphorous from thermally treated sludge and separation of aluminum by adsorption

Because global phosphorus (P) resources are limited, the continued supply of this element is a concern, and the recovery of P from waste is desirable. Carbonized sludge contains aluminum (Al) and iron (Fe) as a result of the addition of coagulants added during dewatering, which hinders the effective use of recovered P. Therefore, it is necessary to develop recovery methods that extract P but not Al or Fe. Zirconium was loaded onto orange waste, a cheap and available agricultural waste in Japan, to investigate the feasibility of its utilization for phosphorus recovery. In the present study, a biomass adsorbent was applied to the selective adsorption of P following extraction using 0.25 mol/l sulfuric acid. This process, based on a batch adsorption system employing a solid-to-liquid ratio of 50 mg/ml or more, was found to adsorb close to 100% of the P but less than 6% of the Al. When the adsorbent was separated and treated with a 0.25 mol/l sulfuric acid solution at a solid-to-liquid ratio of 20 mg/ml, about 75% of the Al was removed but none of the P. Immersion in a NaOH solution was able to strip the P from the adsorbent, giving P and Al concentrations in the desorption solution of 800 and 3 mg/l, respectively.