Purification of aluminium sulphate

摘要

Aqueous aluminium sulphate containing as impurities iron and at least one of titanium and zirconium is purified by (1) adding an oxidizing agent to convert Fe++ to Fe+++, (2) mixing with agitation the oxidized product with a water-insoluble amine anion exchanger to extract the impurities, (3) separating and recovering the purified aqueous aluminium sulphate, (4) reactivating the amine anion exchanger by contacting it with aqueous sulphuric acid (/sF6% conc.), (5) then treating it to reduce the sulphate content to 25% or less based on the weight of amine ion exchanger, (6) recycling the treated ion exchanger to step 1. Oxidizing agents used in steps (1) may be NaClO3, KMnO4, O3 or H2O2, preferably in amounts equivalent to Fe+ + present. The H2O2 if used is preferably 3% by weight, possibly containing a stabilizer, and is reacted pref. at about 45-60 DEG C. The amine anion exchangers used in step (2) may be Diaurylamine, triaurylamine, butyldiaurylamine, "Amberlite" LA-1 (Registered Trade Mark), and are preferably dissolved in an organic solvent, e.g. petroleum distillates, aliphatic and aromatic hydrocarbons, alcohols, kerosene, heavy naphtha, benzene. The conc. of exchanger is pref. 2-30%. In step (2) the aqueous/organic phase ratio may be in the range 1 : 25 to 3 : 1. Step 5 may be carried out by washing with water. For example, on the flow diagram, which illustrates counter-current extraction and regeneration, an aluminium sulphate liquor charge from the digestion of clay or bauxite containing iron, zirconium and titanium impurities leaves tank one via line 2, is admixed with 3% H2O2 from tank 3 introduced via line 30, and the oxidation is completed in tank 6. The oxidized mixture then flows, via line 7, through mixer settlers 8, 9, 10, 11 and 12 respectively countercurrent to an amine ion exchanger, e.g. Amberlite LA-1 dissolved in kerosene, introduced through line 35. The purified aluminium sulphate solution is then passed through stripping towers 39 and 41 (e.g. packed with granular carbon) to remove kerosene. Pregnant amine ion exchanger solution passes from mixer settler 8 to mixer settlers 23, 24 where it is regenerated by a countercurrent stream of 10-15% H2SO4 introduced through line 43 and withdrawn through line 48. The amine is then washed with water introduced from line 44 and withdrawn from line 45 to reduce the sulphate content to 12% based on the weight of the amine. The regenerated amine is then recycled via pump 33 and line 35.