Study On The Purification Of Wet-process Phosphoric Acid By Solvent Extraction

Wet-process phosphoric acid (WPA) is generally used for making phosphorus fertilizers because of high impurity contents. If we want to make high-quality phosphate products, the wet-process phosphoric acid is required to be further purified.Many domestic and international engineers have made lots of works on the purification of wet-process phosphoric acid. One of the most successful technologies is solvent extraction which has already applied to industrial production. Domestic engineers have studied on this topic to some extent, but these studies are only limited to lab scale. We have not seen the relative reports on successful industrial pilot yet. And the ripe technologies of wet-process phosphoric acid purification are kept secret very much abroad; the patent fee is very high. So it is necessary for us to develop our own technology for wet-process phosphoric acid purification, in order to keep up with domestic fast-developing wet-process phosphoric acid industry, and to meet the increasing demand for industrial phosphoric acid and food phosphoric acid.This paper has developed a new technology for wet-process phosphoric acid purification through the purification researches on wet-process phosphoric acid offered by Guizhou Hongfu Co., Ltd. In this technology, TBP is adopted as extraction solvent, the wet-process phosphoric acid offered by Guizhou Hongfu Co., Ltd is used as raw materials, the quality of purified phosphoric acid can meet industrial standardson furnace-process phosphoric acid through pretreatment, extraction, washing, and reverse extraction. Its technological process is shown in the following figure. This technology has the following two main advantages. First, this technology has carried out discoloration, desulphurization and defluorination in one step whose results are superior to the results carried out step by step, and then has simplified the technology. Second, since there is no need to recover solvents by adopting TBP as extraction solvent, this technology has simplified the procedure, reduced energy consumption and the cost.Through experiments, we have determined the optimum operation parameters for pretreatment. The optimum reaction temperature is 60; reaction time is 4.5 hours; Mixing speed is 300 rpm; The E type active carbon: 0.5% (counted by acid quality); Phosphorus ore: 1.24 times of theory amount; Sodium carbonate: 120% of the theory amount; Barium carbonate is added in seven minutes before reaction stops. The pre-treated phosphoric acid can meet the requirement of the solvent extraction.The experiment has succeeded in developing new equipment for WPA purification-reciprocating sieve plate column, and has optimized its structural parameters. The plate's hole ratio and the distance between plates are 53% and 7cm, 53% and 8cm, and 45% and 6cm with respect to extraction, washing, and reverse extraction column.By utilizing the operation and structural parameters obtained from this research, we have designed and enlarged the devices for industrial pilot, we have built up an industrial pilot device of 3000t/a (P2O5) in Guizhou Hongfu Co., Ltd. The pilot experiments have shown that the purification cost for each ton products (P2O5) which meet industrial standards on furnace-process phosphoric acid is about 250 Yuan. This proved that the technology for WPA purification developed from this research is economically feasible.