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[3K0111-25-15] Separation of Silicocarnotite and Gehlenite using a kerosene-based extraction process as a route to recover phosphorus from Sewage Sludge Ash

○Edwin Mauricio Cordova Udaeta¹, Toyohisa Fujita¹, Gjergj Dodbiba¹ (1. The University of Tokyo)

司会：芳賀 一寿（秋田大学）、三木 一（九州大学）、 ドドビバ ジョルジュ（東京大学）、大島 達也（宮崎大学）

Keywords:Silicocarnotite, Gehlenite, Phosphate recovery, Kerosene, Liquid-Liquid Separation

In recent times, recovering phosphate from unconventional sources such as Sewage Sludge Ash (SSA) appears as an option to ease the predicted scarcity of this mineral in the future. The present research work studies the separation of a silico-phosphate phase (silicocarnotite, Ca5(PO4)2SiO4), from an aluminum-silicate phase (gehlenite, Ca2Al2SiO7); via a straightforward liquid - liquid separation process using a surfactant (Sodium Dodecyl Sulfate), a coagulation reagent (chitosan) and a solvent (kerosene). If synthetic precursors are used, experiments pointed out that silicocarnotite and gehlenite require temperatures higher than 1200 C° in order to be formed. Zeta potential measurements for these species under different pH conditions, indicated that gehlenite remains negatively charged in the entire range of pH tested (2.5 to 11), whereas silicocarnotite is negative under alkaline and neutral conditions, presenting the point of zero charge (PZC) at around pH = 6. When the extraction process was carried out using a mixture consisting of 2 parts kerosene/7 parts water for an aqueous pulp containing 10 % wt. of solid material; a sample consisting of a 1:1 mix of synthetic silicocarnotite and gehlenite has an enrichment ratio of 1.58 in phosphorus content whenever a dose of 1.44 Kg/ton SDS is used as a surfactant, the pH is equal to 6, and 100 ppm chitosan is added as a coagulation reagent.

When SSA is used as a precursor for silicocarnotite and gehlenite formation, experiments showed that heating a mixture of SSA with Ca(OH)2 at 1300 C°, yields them both simultaneously. Also, experiments performed on this product (named H-Ash), revealed its zeta potential is negative under alkaline conditions with the PZC point at pH = 6.5. Subjecting H-Ash to the extraction process described before results in an enrichment ratio of 1.03 in phosphorus content, with the reduced effectiveness possibly due to the presence of interfering species.