Boron ores are used in the production of various boron compounds. One of the most important of them is borax obtained from tincal During borax production a large quantity of the boron oxide (B2O3) is lost with the reactor waste, Also, this waste causes different environmental problems when it discharged directly to the environment, In this study, the evaluation of the reactor waste in borax production was investigated to recover B2O3 and therefore to reduce the toxic effect of the waste. For this purpose, the reactor waste was leached by SO2-saturated water. It was found that about 90 % of B2O3 in the waste was recovered. In addition, about 80 % of CaO in the waste was dissolved in the leaching solution. A part of the dissolved CaO precipitated as CaSO3.1/2H(2)O and CaSO4.2H(2)O, and the other part remained as Ca(HSO3)(2) in the solution, It is possible that CaSO3. 1/2H(2)O and Ca(HSO3)(2) can be used in the paper industry and in other some industries. (C) 1999 Elsevier Science Ltd. All rights reserved.