Abstract: Nanofiltration processes using one or more conventional nanofiltration membrane modules under a positive applied pressure is used to selectively change the concentration of one solute, such as sodium chloride or sodium chlorate providing monovalent ions, from another solute such as sodium sulfate or sodium dichromate to provide multivalent ions in high salt aqueous concentrations. The process is particularly useful in favourably lowering the concentration of undesirable ions, particularly, of silica and dichromate ions in chloralkali and chlorate brine containing solutions and favourably raising the sodium sulphate level relative to sodium chloride in chloralkali liquor.

Abstract: Improved environmentally acceptable process for retaining chelant-containing effluent within pulp bleach plants, particularly total chloride-free bleaching sequence plants using a chelating agent closed re-cycle process. The process involves treating a pulp liquor in an acidic or near neutral stage with an effective chelating amount of a chelating agent to form a soluble, chelated metal species; removing the pulp to provide a chelated metal species-containing solution; treating this solution in an alkaline stage in the presence of sufficient Ca ions with an effective amount of an alkaline liquor to effect displacement of metals from the chelated metal species and precipitation of the metals as solids in alkaline solution; removing the solids from the alkaline solution to provide a metal-free, chelating agent-containing solution; and recycling the metal-free solution to the pulp liquor.

Abstract: Process for the removal of heavy metal, metalloid and fluoride species present in trace mounts from aqueous brine of use in the production of chlorine and sodium hydroxide by electrolysis in membrane cells or in chlorate production; particularly to said removal by adsorption on hydroxyapatite; and more particularly to adsorption on bone charcoal.

Abstract: A method for removing sulphate ions from an aqueous solution of an alkali metal halide containing sulphate ions, which method comprises contacting said solution with a particulate, composite ion-exchange material comprising a hydrous oxide of a metal selected from the group consisting of titanium, zirconium and cerium, dispersed on a support comprising a brine solution compatible material. Preferably the compatible material is selected from hydrous oxides of titanium, cerium and zirconium. An improved cost-effective practical method of sulphate removal is provided.

Abstract: A nanofiltration process using a conventional nanofiltration membrane module under a positive applied pressure is used to selectively change the concentration of one solute, such as sodium chloride or sodium chlorate providing monovalent ions, from another solute such as sodium sulfate or sodium dichromate providing multivalent ions in high salt aqueous concentrations. The process is particularly useful in favourably lowering the concentration of silica and dichromate ions in chloral kali and chlorate brine containing solutions and favourably raising the sodium sulphate level relative to sodium chloride in chloraldhali liquor. The relatively high salt concentration, surprisingly, effects little or no monovalent, particularly, Cl.sup.- rejection.

Abstract: A method and apparatus for producing hydrogen peroxide in caustic solution utilizing an electrolytic cell having electrolytes, preferably, alkaline in both anode and cathode compartments separated by a bipolar membrane which splits water into hydrogen ions and hydroxyl ions. Electrolysis of oxygen which diffuses through a gas-diffusion cathode forms peroxide in catholyte while hydrogen ions generated within the bipolar membrane migrate into the catholyte. Peroxide can be produced in the catholyte as a cell product having a caustic to peroxide ratio of less than 1.0 at five percent peroxide, by weight.

Abstract: Methods for the electrolysis of aqueous solutions of alkali metal carbonates and bicarbonates for the production of alkali metal hydroxides at current efficiencies of >85 percent without the simultaneous co-production of halogen or acid can be performed at very low, commercially attractive cell voltages and at high current densities in single or two solution compartment cells with carbon dioxide as the only substantive co-product by maintaining cell pH at >7. The methods are also especially suitable for retrofitting existing chlor-alkali facilities for shifting the balance of production in favor of caustic soda at peak demands. The methods may also be performed with fuel cell configurations for even more attractive operating economics.

Abstract: Process for separating sulphate from a contaminating chromium component contained in an aqueous liquor by the crystallization of a sulphate compound. The sulphate may be separated substantially free of chromium component by adjustment of the pH to the range of from about 2.0 to about 6.5, followed by cooling of the liquor to precipitate the sulphate compound from solution which sulphate is subsequently removed. The process provides an effective method for the separation of sulphate from dichromate, and is particularly useful in the production of chlorate.

Abstract: A process for the recovery of sulphuric acid from a waste acid stream containing ammonium sulphate comprising vaporizing the waste acid and subsequently converting the ammonia and sulphur dioxide generated to nitrogen and sulphur trioxide, respectively. The process provides an economic method for the regeneration of the waste sulphuric acid from a methyl methacrylate production process.

Abstract: Apparatus for the manufacture of sulphuric acid comprising at least one gas-concentrated sulphuric acid contacting unit and a sulphuric acid heat exchanger. The contacting unit and/or the heat exchanger is formed of high silicon content austenitic steel.

Abstract: Metal electrodes provided with a coating consisting essentially of a mixed oxide compound of (i) a compound of the general formula ABO.sub.4, having a structure of the rutile-type, where A is an element in the trivalent state selected from the group consisting of Al, Rh and Cr, and B is an element in the pentavalent state selected from the group consisting of Sb and Ta, (ii) RuO.sub.2 and (iii) TiO.sub.2 ; wherein the mole fraction of ABO.sub.4 is between 0.01 and 0.42, the mole fraction of RuO.sub.2 is between 0.03 and 0.42, and the mole fraction of TiO.sub.2 is between 0.55 and 0.96. The electrodes have low precious metal content, provide improved durability and improved current efficiency-anodic overvoltage performance. They are used in the electrolysis of chloride containing liquors in the production of, for example, chlorine and more particularly, chlorate.