Method of preparing wet process phosphoric acid

A process for preparing phosphoric acid, which comprises:

• decomposing phosphate rock, separating the decomposed solution, converting the dihydrate gypsum and filtrating, is characterized in that, the process comprises the steps following:
• (1-1) in a first reactor (1), feeding phosphate rock slurry, sulfuric acid, and recycled low-concentration phosphoric acid (9) from a filter to conduct decomposition;
• and obtaining a first reaction solution;
• wherein the weight ratio of phosphate rock slurry to sulfuric acid to recycled low-concentration phosphoric acid is 1:
• (0.6–0.8):
• (1.0–2.5);
• (1-2) in a second reactor (2), feeding the first reaction solution obtained in step 1-1, and other phosphate rock slurry and sulfuric acid thereby making the reaction complete;
• (1-3) dividing the reaction solution obtained from the second reactor into two parts:
• one part (8) comprising 10–30% of the reaction solution flows into conversion cell (4), and the other (7) flows into a separator (3), wherein the product phosphoric acid is extracted;
• (1-4) in a conversion cell (4), feeding the dihydrate gypsum (10) separated out from the separator, some additional sulfuric acid and the one part (8) of the second reaction slurry from the second reactor to conduct the conversion reaction;
• and obtaining a conversion solution;
• and
• (1-5) in a filter (6), after filtering the conversion solution, feeding the filtrate (9) into the first reactor;
• wherein the filter cake is the crude low-concentration phosphoric acid hemihydrate gypsum useful for producing sulfuric acid and cement.