Abstract: Sulfuric acid contaminated with boron and fluoride values such as the waste acid of a boron trifluoride process is purified by contacting the contaminated acid with an inert gas to desorb boron trifluoride, and the inert gas is stripped by contacting with an absorbing liquid including concentrated sulfuric acid. Hydrogen fluoride and/or fluorosulfuric acid are added to contaminated sulfuric acid as agents to spring non-volatile boron value. In addition, the water content of the contaminated acid is adjusted within a narrow concentration range, to improve the efficiency of both the stripping and the absorption operations. The absorption of boron trifluoride into the absorbing sulfuric acid is improved when it contains boric acid. Preferably the contaminated sulfuric acid to be purified is one portion of the waste liquid and the absorbing liquid is another portion of the waste liquid of a boron trifluoride manufacturing process.

Abstract: In the process of making aqueous alkali metal hydroxide solution and diatomic halide gas by electrolysis of aqueous alkali metal halide solution in a bank of cationic permselective membrane cells, current efficiency is improved and/or concentration of the alkali metal hydroxide solution product is increased by feeding water to the cathode compartment of the first cell and then transferring the catholyte serially from cell to cell at incrementally increasing alkali metal hydroxide concentration, and withdrawing alkali metal hydroxide product solution from the last cell of the bank.