Phosphate recovery from waste fish bones ash by acidic leaching method and iron phosphate production using electrocoagulation method

Abstract

This study aims to test three different acids (HCl, H2SO4, HNO3) for phosphate (PO4−3) extraction from waste fish bones ash using response surface methodology (RSM). Moreover, PO4−3 recovery from the P-rich solution as iron(III) phosphate (FePO4) was carried out using iron-supported electrocoagulation process (EC) with a Box-Behnken Design. The results showed that nitric acid (HNO3) supplied better phosphate extraction compared to hydrochloric acid (HCl) and sulfuric acid (H2SO4). Approximately 97.5% of PO4−3 was recovered in the form of a rich PO4−3 extraction solution using 6 M HNO3 and an acid-ash ratio of 13.7 kg acid/kg ash. The maximum recovery efficiency of phosphate (100%) was achieved at pH 4.96 and current density of 5.96 V, time of 60 min in the EC process. The operating cost of the EC process was calculated as 1.63 US$/kg PO4−3. Iron phosphate obtained in different time periods under optimum conditions were characterized by X-Ray Diffraction (XRD) analysis. According to XRD results, three different iron phosphate (lipscombite, iron(III) phosphate(V), and heptairon pentaphosphate hydrogen phosphate) were obtained. The present study suggested that P recovery from waste fish bones ash using acid leaching method and production of iron phosphate using the electrocoagulation process could be considered as a cleaner production. In addition, the study presents an environmentally and sustainable method for the recovery of phosphate resources.