C-i-l, Inc.

Cominco, Ltd.

Ian H Warren

Felix Mok

Kin Seto

John E Burkell

A process for removing dichromates from chlorate-rich solutions containing hypochlorite and dichromate ions and produced by the electrolysis of brine. The dichromate is reduced in a two-stage process by the addition of ammonia under controlled conditions of pH and temperature to a mixed di- and trivalent chromium hydroxide which is precipitated from solution and removed. The process provides an economical method of recovering chromium from electrolytically produced chlorate solutions.

Stripping and recovery of dichromate in electrolytic chlorate systems

Process for the production of sodium chlorate by the electrolysis of sodium chloride contaminated with sodium sulphate wherein the sulphate concentration in the system is kept below a pre-selected level. A portion of the mother liquor remaining after crystallizing out some of the sodium chlorate product is selectively further cooled to effect crystallization of some of the sodium sulphate present in the liquor. An acceptable 'steady-state' concentration of sulphate ion is established which prevents the deleterious excess sulphate ion build-up in the electrolytic system.

Production of sodium chlorate

Certain continuous methods for monitoring the quality of ZnSO.sub.4 electrolyte lose sensitivity when the electrolyte contains Sb (V). The sensitivity can be increased by electrochemically reducing Sb (V). A sample of electrolyte which contains impurities including Sb (V) and which may also contain polarization affecting agents is passed through a test cell containing an elongated moving cathode having a predetermined area exposed to the electrolyte, an anode and a reference electrode. A substantially constant current in the range of 0.01 to 0.20 A/cm.sup.2 is applied to the electrodes and the cathode is moved with a speed sufficient to obtain measured values of the cathode polarization potential of zinc deposition on zinc. The measured values are related to the concentrations of impurities, polarization affecting agents, or both and to the concentration ratio between impurities and polarization affecting agents, and the process for zinc recovery is adjusted in response to these relations to obtain optimum zinc recovery.

Method for monitoring the quality of ZnSO.sub.4 electrolyte containing

A composite electrode made up by stacking a multiplicity of alternate anode plates and cathode plates the adjacent surfaces of which are insulated from each other by a thin film of an insulating material such as fluon, kynar, PVC, etc. With this composite electrode, a K value of 0.100 to 0.150 can be easily achieved in the electrolytic production of chlorates and hypochlorites.

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Richmond, Canada

Ian H Warren