CONCN. AND PURIFICN. OF SULPHURIC ACID FROM TITANIUM DI:OXIDE MFR. - by boiling in presence of ferrous sulphate to remove chromium

摘要

The process concerns the removal of Cr ions in the concn. of dil. H2SO4 solns. contg. FeSO4 from TiO2 pigment mfr. by evapn. of water and sepn. of FeSO4, the soln. being conc. to 60-70 wt.% H2SO4, as in DT 2618121. The novelty is that the dil. or pre-conc. acid, contg. is not 500 g. FeSO4/g. Cr to be removed, is kept at the boil at is not 130 degrees C. Cr is pptd. if the required amt. of FeSO4 is present and better pptn. is attained at higher temps. Higher temps. also favour the pptn. of FeSO4.H2O in easily filtered form. The FeSO4 content can be controlled by selection of the crystallisation conditions for FeSO4.(H2O in pigment mfr. or by adding solid hydrated FeSO4 to the dil. acid before concn. After sepn. of the pptd. metal salts, the conc. 60-70% acid pref. is treated with solid hydrated FeSO4 to give up to 2000 g. FeSO4/g. Cr to be removed and then boiled for 2-4 hr., after which the FeSO4 added and other pptd. metals salts are sepd.