A SO(4)(2-)contg. wastewater from prodn. of printed circuit boards was treated with a spent bath from Al etching, Ca(OH)(2) and NaOH or HCI at 19 degrees C and pH 11.2-12.0 for 30 min (Al3+ concn. 0.148-0.228 mg/L, Ca2+ concn. 0.633-1.033 mg/L) to study the pptn. of 3CaO center dot Al2O3 center dot 3CaSO(4)center dot 32H(2)O. The SO42- concn. in the system decreased from 1035 mg/L down to even 46 mg/L. The results were presented as polynomial regression equations. The concn. of Cu2+ ions in the system also decreased from 1.6 mg/L down to 0.9 mg/L with the increasing pH (from 10.93 up to 12.27).