Purification of recovered phosphoric acid by extracting aluminium with di-2-ethylhexyl phosphoric acid

Abstract

The extraction of aluminium from dilute phosphoric acid with di-2-ethylhexyl phosphoric acid (DEHPA) was optimized using response surface methodology. The optimization was based on the experimental three-level central composite face-centred design (CCF) and was conducted on real-life samples. The three variables included were pH, extractant concentration and aqueous to organic phase ratio (AO). Under the optimized conditions (pH 2.5, 0.6 M DEHPA and AO ratio 1:2), extraction efficiency of 99% for aluminium in four extraction stages is achieved. The purified phosphoric acid solution can then be utilized by the fertilizing industry. Stripping tests for organic phase loaded with aluminium were conducted with sulphuric acid. Extremely high stripping efficiency was obtained with 0.9 M sulphuric acid resulting in the recovery rate of 88% in one stage. After stripping, the aluminium sulphate solution can be reused as a precipitation agent for phosphorus in the wastewater treatment process.