Amino-poly:carboxylic acid, esp. EDTA, recovery from aq. soln., esp. flue gas scrubbing liquor

摘要

In the recovery of aminopolycarboxylic acids (I), esp. EDTA, by acid pptn. of the free acid from aq. soln., SO2 is introduced to reduce the pH to less than 2 and ppte. the free acid, which is filtered and dried, opt. after washing, whilst the filtrate is discharged. The free acid is pptd. at a temp. below 60 deg C, esp. at 30-40 deg C. Introduction of SO2 is carried out in a vessel kept under slight vacuum, pref. in the absence of O2, and excess SO2 is discharged. The recycled soln. contains Na2SO3, Na2S2O5, Na2S2O3 and/or Na2SO4. The filtrate is calcined to liberate the bound SO2, which is recovered in the flue gas desulphurisation plant. The plant cake is recycled with the alkaline aq. soln., so that (I) is brought into soln. as its alkali salt.