Boron ores are one of the most important underground richness of Turkey. Various boron compounds are produced from these ores. The most important one of them is borax. During the borax production process, a large quantity of the boron oxide (B2O3) is discharged by the trommel sieve waste (TSW). Also, this waste causes different environmental problems when it discharged directly to the environment. In this study, evaluation of the reactor waste discharged directly to environment during borax production was investigated to recover B2O3 and therefore to reduce the toxic effect of the waste. For this purpose, the TSW was leached by SO2-saturated water at various experimental conditions. It was found that the 90% of B2O3 in the waste was recovered. In addition, about 80% of CaO in the waste dissolved in the leaching solution. A part of the dissolved CaO converted to CaSO3 . (1)/2H2O and Ca(HSO3)(2) which can be used in the paper industry and in other some industries. (C) 2002 Elsevier Science B.V. All rights reserved.