GB1025282A - Improvements in or relating to the treatment by electrolytic oxidation of cyanide wastes - Google Patents

Abstract

Cyanide wastes are treated to provide a solid product free from cyanides and cyanates by electrolytically oxidizing an aqueous solution of the waste at an elevated temperature, removing liquid from the electrolytic cell and cooling it to crystallize out dissolved carbonate, separating the carbonate and returning the liquid to the cell, and adding cyanide waste to maintain largely constant the cell concentration of cyanide. Preferably the cyanide concentration is at least 10 gm. HCN per litre and electrolysis is effected at a temperature of 60 to 95 DEG C. with an anode current density of 10 to 230 ASF using graphite or platinum metal coated titanium, while all the treatment stages are continuously operated. Fig. 1 (not shown) relates to a simple apparatus in which the electrolytic cell containing NaCN wastes in solution has an immersed heating coil fed with hot water while the crystallizing unit has a cooling water jacket, stirrers being provided in both the cell and the crystallizer, and cyanide waste is added to the filtrate before this is pumped back to the cell. In the arrangement of Fig. 2, the gases evolved from the thermally insulated cell 13 are fed through a condenser 21 and a scrubber 23 fed with sodium carbonate solution and escape of hydrogen cyanide is thereby prevented, being either returned directly to the cell in solution or with the scrubbing solution via sump 27. Sodium carbonate crystals from the crystallizer 17 are fed to a vacuum-assisted filter 19 from which the filtrate and crystal washings are fed to the sump 27 the level in which is kept constant by adding water via a float-controlled valve 29a. Hydrogen leaving the scrubber 23 is burnt at 26 to pre-heat the liquid to be returned to the cell along pipe 15 from the sump, sodium cyanide solution being added to it along pipe 32. In the electrolysis, sodium oxalate and urea are also formed in minor amounts, and the sodium carbonate crystals contain small amounts of sodium oxalate and cyanides (0.05% HCN). <PICT:1025282/C6-C7/1>