Recovery of phosphorus from sewage sludge ash by heat treatment and liquid-liquid separation

Phosphorus is a scarce resource, some estimates predict a peak in production in the years to come; therefore, research efforts on methods to recycle the phosphate generated in urban sewage are increasing. Sewage Sludge Ash (SSA) arises as a promising source for Phosphorus Recycling. This research studies the use of a Heat Treatment, followed by liquid-liquid extraction in order to attain P205 recovery from SSA. The heat treatment was carried out using the addition of Ca(OH)₂ and exposure to 1250° C for 30min, in order to form the P-bearing phase Silicocarnotite (Ca₅(PO₄)SiO₄) and a phase similar to the non P-bearing phase Gehlenite (Ca₂Al₂SiO₇). Preliminary experiments have shown that these mineral phases can be separated using a simple extraction using kerosene and a surfactant under controlled pH. When the actual SSA sample was heated this way and then subjected to extraction, a maximum difference of 39% in P₂O₅ content was obtained at pH = 2 when 0.25% Dodecyl Amino Acetate (DAA) is used as surfactant.