The effects of phosphate concentration on the recovery of phosphate from alkaline solution by hydrated lime and calcined oyster shell: recovery efficiency, capacity and hydroxyapatite purity

Abstract

Phosphate recovery from wastewater can solve the problems of both phosphate pollution and phosphate resource depletion. The main obstacle to phosphate recovery is the high cost. Most of studies focus on phosphate removal from sewage. Adsorption by metal oxide is a promising method for phosphate removal. In order to reuse the adsorbent, the exhausted adsorbents are usually regenerated with alkaline solution. This paper proposed a ''Double Adsorption'' method that combing the phosphate removal by metal oxide adsorption and the phosphate recovery from the alkline regenerated solution by Ca(OH)2 adsorption. This method has the advantage of low effluent phosphate level, low cost and no secondary pollution. To test this method and the possibility of using oyster shell to recover phosphate from the regenerated alkaline solution, the effect of phosphate concentration on the phosphate recovery efficiency and hydroxyapatite purity were studied in this paper. The results show that both the hydrated lime and oyster shell have high phosphate recovery capacity in alkaline solution, and the high phosphate concentration samples have low phosphate recovery efficiency and high hydroxyapatite purity, and vice versa. Both the hydrated lime and calcined oyster shell can be used to recover phosphate from alkaline solution. This study proves that the ''Double Adsorption'' method is feasible and can promote the realization of phosphate recovery.

Keywords

• Phosphorus recovery
• Hydrated lime
• Oyster shell powder
• Phosphorus crisis
• Hydroxyapatite formation
• Adsorption