Recovery of Cerium Salts from Sewage Sludge Resulting from the Coagulation of Brewery Wastewater with Recycled Cerium Coagulant.

Due to the high cost and limited sources of cerium coagulants, it is extremely important to take measures to recycle this raw material. This paper presents the new possibility of recovering cerium(III) chloride, cerium(III) sulphate, cerium(IV) sulphate, and potentially phosphate from sewage sludge (101.5 g/kg Ce and 22.2 g/kg total P) through a brewery wastewater treatment process using recycled CeCl 3 as a coagulant. In order to recover the Ce and P, the sludge was subjected to extraction using an HCl solution. Optimal process conditions were determined by means of central composite design and response surface methodology (CCD/RSM) for three input parameters (HCl mass, reaction time, and extractant volume). Under optimal conditions (0.35 g HCl per 1 g of sludge, 40 min reaction time, extractant volume of 25 mL per 1 g of sludge), the highest efficiency obtained was 99.6% and 97.5% for Ce and P, respectively. Cerium(III) oxalate as Ce 2 (C 2 O 4 ) 3 ∙10H 2 O was precipitated from the obtained solution using H 2 C 2 O 4 (99.97%) and decomposed into CeO 2 (at 350 °C), which was afterwards subjected to a reaction with HCl (30%, m/m) and H 2 O 2 (30%, m/m), which led to the crystallisation of CeCl 3 ∙7H 2 O with a purity of 98.6% and a yield of 97.0%. The obtained CeO 2 was also subjected to a reaction with H 2 SO 4 (96%, m/m) and H 2 O 2 (30%, m/m), which produced Ce 2 (SO 4 ) 3 with a yield of 97.4%. The CeO 2 was also subjected to a reaction with only H 2 SO 4 (96%, m/m), which produced Ce(SO 4 ) 2 with a yield of 98.3%. The filtrate obtained after filtering the Ce 2 (C 2 O 4 ) 3 ∙10H 2 O contained 570 mg/L of P, which enabled its use as a source of phosphorus compounds. The presented processes of Ce and potentially P recovery from sewage sludge originating from brewery wastewater contribute to the idea of a circular economy.