An efficient process for preparation of potassium thiosulfate (K.sub.2S.sub.2O.sub.3) is described. Potassium hydroxide (KOH) and elemental sulfur (S) are converted to potassium polysulfide, which is subsequently oxidized. The process allows using specifically designed process conditions such as mole ratios of potassium hydroxide to sulfur, and temperature, to obtain an optimized formulation of desired polysulfide, and a specifically designed set of conditions such as temperature, pressure, rate and duration of the oxidant during the oxidation conditions, to obtain a relatively high concentration of soluble potassium thiosulfate product with high purity, with relatively low amounts of byproducts. The manufacturing process can either be a batch process or a continuous process utilizing Continuous Stirred Tank Reactors (CSTR). The CSTR process is dependent on several design parameters, including pressure, and temperature optimization to avoid product instability. The resulting potassium thiosulfate is a beneficial fertilizer with high potassium content as a 50% liquid source of potassium.

A method of regenerating an activated carbon catalyst which is used in the production of polysulphide liquor. In the method, the catalyst is washed with a washing liquid in order to remove the sediment accumulated in the catalyst. According to the present invention, in this case, the activated carbon catalyst is regenerated most suitably by bringing it to a multi-stage washing which comprises at least one washing step in which the washing liquid used comprises sodium sulphide, and one washing step in which acidic washing liquid is used. The sulphur precipitate is peeled off using sodium sulphide, and the iron and other metals can be effectively removed by using an acidic washing, without damaging the catalyst.

A method of regenerating an activated carbon catalyst which is used in the production of polysulphide liquor. In the method, the catalyst is washed with a washing liquid in order to remove the sediment accumulated in the catalyst. According to the present invention, in this case, the activated carbon catalyst is regenerated most suitably by bringing it to a multi-stage washing which comprises at least one washing step in which the washing liquid used comprises sodium sulphide, and one washing step in which acidic washing liquid is used. The sulphur precipitate is peeled off using sodium sulphide, and the iron and other metals can be effectively removed by using an acidic washing, without damaging the catalyst.

The present addresses the problem of providing a new method for producing a metal and/or metalloid-containing sulfide. The problem is solved by a method for producing a metal and/or metalloid-containing sulfide characterized by using as a reaction medium and sulfur source a melt that can be obtained by heating a first sodium polysulfide represented by Na.sub.2S.sub.x (in the formula, 1<x5) and synthesizing a sulfide containing a metal and/or metalloid (where the metal is neither an alkali metal nor an alkaline earth metal) under normal pressure.

The present addresses the problem of providing a new method for producing a metal and/or metalloid-containing sulfide. The problem is solved by a method for producing a metal and/or metalloid-containing sulfide characterized by using as a reaction medium and sulfur source a melt that can be obtained by heating a first sodium polysulfide represented by Na.sub.2S.sub.x (in the formula, 1<x5) and synthesizing a sulfide containing a metal and/or metalloid (where the metal is neither an alkali metal nor an alkaline earth metal) under normal pressure.

Alkali metals and sulfur may be recovered from alkali monosulfide and polysulfides in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.

Alkali metals and sulfur may be recovered from alkali monosulfide and polysulfides in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.

An efficient process for preparation of potassium thiosulfate (K.sub.2S.sub.2O.sub.3) is described. Potassium hydroxide (KOH) and elemental sulfur (S) are converted to potassium polysulfide, which is subsequently oxidized. The process allows using specifically designed process conditions such as mole ratios of potassium hydroxide to sulfur, and temperature, to obtain an optimized formulation of desired polysulfide, and a specifically designed set of conditions such as temperature, pressure, rate and duration of the oxidant during the oxidation conditions, to obtain a relatively high concentration of soluble potassium thiosulfate product with high purity, with relatively low amounts of byproducts. The manufacturing process can either be a batch process or a continuous process utilizing Continuous Stirred Tank Reactors (CSTR). The CSTR process is dependent on several design parameters, including pressure, and temperature optimization to avoid product instability. The resulting potassium thiosulfate is a beneficial fertilizer with high potassium content as a 50% liquid source of potassium.

Alkali metals and sulfur may be recovered from alkali monosulfide and polysulfides in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.

Alkali metals and sulfur may be recovered from alkali monosulfide and polysulfides in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.