Sulphuric acid demetallisation in titanium dioxide pigment mfr. - by continuous addn. to metal salt suspension in conc. acid and evapn.

摘要

Removal of undesirable metal ions, esp. Cr ions, in the concn. of dil. sulphuric acid (I) solns. contg. Fe (II) sulphate (II) by evapn. and sepn. of (II) to a (I) content of 60-70 wt.% involves continuous introduction of the fil. (I) soln. or a preconcentrate obtd. without pptn. of metal salts into a (I) contg. metal salt (III) suspension contg. 60-70 wt.% (I), without addn. of clarified (I) (soln.). Water is evaporated so that the (I) content is kept at 60-70 wt.%. Part of the (I)-contg. (III) suspension is removed continuously or at intervals and the pptd. (III) is sepd. In an example, a simple concn. process was used, and only 33% of the Cr present was pptd., whereas addn. of the dil. acid to 64% (I) boiling at 27 mbar (65 degrees C) gave 71% removal of Cr and 88% removal of V. Used in the purificn. of (I) soln. obtd in Ti dioxide pigment mfr. The acid can be recycled without further concn. or pyrificn. and the capital costs and energy consumption are low.