Abstract: Disclosed is a method of treating an electroless nickel plating bath mainly containing a water-soluble nickel salt, a complexing agent for complexing the nickel salt, and sodium hypophosphite as a reducing agent for reducing the nickel salt, including the steps of:repeatedly regenerating and reusing the electroless nickel plating bath in which a phosphite is accumulated by adding nickel sulfate to the plating bath to produce and precipitate nickel phosphite and separating the nickel phosphite from the plating bath; and adding sulfuric acid or a mixture of sulfuric acid and sodium sulfate to the nickel phosphite separated from the plating bath to convert the nickel phosphite into nickel sulfate and phosphorous acid or NaH.sub.2 PO.sub.3, and recovering the nickel sulfate.

Abstract: The brine purifying system employs a multistage filtering apparatus comprising a plurality of the same filter units piled up one over another to form a plurality of cascaded filtering stages. When the filter layers of the filter units are clogged with unsoluble matters, the operation of the multistage filtering apparatus is interrupted, then a solvent for the unsoluble matters is circulated through the multistage filtering apparatus to remove the unsoluble matters arrested by the filter layers by dissolving the same therein. Then, a washing liquid is circulated through the multistage filtering apparatus to wash the multistage filtering apparatus completely. The solvent and the washing liquid used for regenerating and washing the multistage filtering apparatus are recovered and are used for dissolving salt to prepare saturated brine. The unsoluble matters thus removed from the filter layers are removed by being precipitated in a precipitating tank.

Abstract: The brine purifying system employs a multistage filtering apparatus comprising a plurality of the same filter units piled up one over another to form a plurality of cascaded filtering stages. When the filter layers of the filter units are clogged with unsoluble matters, the operation of the multistage filtering apparatus is interrupted, then a solvent for the unsoluble matters is circulated through the multistage filtering apparatus to remove the unsoluble matters arrested by the filter layers by dissolving the same therein. Then, a washing liquid is circulated through the multistage filtering apparatus to wash the multistage filtering apparatus completely. The solvent and the washing liquid used for regenerating and washing the multistage filtering apparatus are recovered and are used for dissolving salt to prepare saturated brine. The unsoluble matters thus removed from the filter layers are removed by being precipitated in a precipitating tank.