Compared with ordinary aluminum sulfate, iron-free aluminum sulfate contains less or no iron and is purer. Iron-free aluminum sulfate can be used in the production of high-grade paper, high-grade fabrics, food leavening agents, white rubber, white leather, etc.
Compared with ordinary aluminum sulfate, the production of iron-free aluminum sulfate requires one more iron removal process. The main methods are as follows:
1. Potassium permanganate iron removal method
Use aluminum hydroxide to adjust the pH of the aluminum sulfate solution to 3.0. Under heating conditions, use 5% (mass fraction) potassium permanganate solution to oxidize divalent iron to trivalent iron to generate ferric hydroxide and manganese dioxide precipitates. Cool to 60°C, filter, discard the filter residue to achieve iron removal, and concentrate and crystallize the filtrate to obtain the finished product. After aluminum sulfate is oxidized and iron removed with potassium permanganate, the iron mass fraction can be reduced to less than 0.01%, thereby achieving the goal of producing low-iron aluminum sulfate products.
2. Solution extraction method
Iron extraction is complex. It is affected by various media conditions, the structure of the extraction agent, the composition of the extraction system, and other factors. Therefore, the application of the extraction method must be conducted through in-depth and detailed research based on specific situations, and it must undergo a certain scale of experiments before it can be applied in industry.
After the aluminum sulfate solution is oxidized with H:O:, a sulfonated kerosene solution containing 20% (mass fraction) N1923 of 2608 is added for extraction. The resulting water phase is the aluminum sulfate solution, which is concentrated to obtain refined aluminum sulfate. Dilute sulfuric acid is added to the organic phase for 4-stage countercurrent extraction to recover the organic extractant. Taking primary amine extraction as an example, after iron removal through extraction with primary amine N1923 and sulfonated kerosene organic solvent, the aluminum sulfate solid appears as white fine-grained crystals. Fe:O in aluminum sulfate after iron removal. The mass fraction can be reduced to 0.051%.