Waster brine contg. NaCl 22,91, (Na2SO4Na2CO30.6)-Na-5.06 and NaOH 0.23 wt.%, pH 11.9, crude or neutralized with 0.4% H2SO4 to pH 7, was desilted, treated with an ammonia soda process spent liquor (contg. the precipitant. in 40-50% excess) to yield a suspension of CaSO4.2H(2)O and CaCO3, 2.8-4.8% solids, in a 1039-12.5% NaCl-CaCl2 soin. This was filtered, CaCO3 was pptd., the ppt. was allowed to settle, whizzed, and dried to yield a 0.17% SO4 brine that could be recycled. This procedure enables at least 23,000 ton NaCl to be recycled annually and waste brine vol. to be reduced by 70-80% Isohydric crystn. of Na2SO4.(H2O)-H-10 for 7200 s at 1degreesC reduced the concn. of Na2SO4 to 1.6-2.0% only.