Ozonation of cyanide with emphasis on gold mill wastewaters

Abstract

Mass transfer ami treatability studies were conducted in a stirred Danckwerts cell to investigate the ozonation of 1) simple cyanide, NaCN, and 2) cyanides found in the barren bleed of Giant Yellowknife Mines Limited. A theoretical analysis of the simultaneous absorption and reaction of ozone in a NaCN solution was used to calculate an overall second order rate‐constant for the reaction with ozone. The order of magnitude value at 23°C is 104 to 105 L/(mol.s). Enhancement factors for the ozonation of the barren bleed are in the range of 80 to 300 for bulk total cyanide concentrations of about 38 to 195 mg/L respectively. Attainable treatment levels for cyanide and thiocyanate and stoichiometric relationships are presented along with an economic assessment for an ozone installation for the Giant Yellowknife Mines Limited case.

Oxidation of cyanides in industrial wastewaters by ozone

“…Similar experiments conducted at pH 2.5, where decomposition ofozone is negligible [8], and cyanide is primarily in the form of HCN, showed that the reaction of molecular ozone with HCN is very slow. On the other hand, when kobs was plotted as a function of cyanide ion concentration,…”

“…However, the lack of information on the chemical kinetics and the mechanism of the ozonation reactions of cyanide compounds has limited the widespread application of ozone by preventing engineers from making reliable design decisions and cost estimations. Previous researchers [1][2][3][4][5][6][7][8], investigating the ozonation of cyanides in semibatch or continuous-flow reactors, have generated rate equations oflumped parameters which combine the kinetics of chemical reactions and the kinetics of ozone absorption, and are therefore empirical and system-specific. Furthermore, there is disagreement in the literature as to the effects of metal complexation of cyanide on the reaction kinetics [3, 4, 61.…”

Review of the Impact on Water Quality and Treatment Options of Cyanide Used in Gold Ore Processing

“…Ozone is a superior oxidant to oxygen and has been extensively studied in the oxidation of cyanide [48][49][50][51]. Two oxidation mechanisms of cyanide to cyanate by ozone have been proposed, namely simple (Eq.…”

Pretreatment with Ozone for Gold and Silver Recovery from Refractory Ores

“…Some research work has been done regarding the use of ozone in the mineral industry, mainly on the treatment of effluents containing cyanide (Mathieu, 1977;Rowley and Otto, 1980), and on the oxidative leaching of copper ores (Roca et al, 2000). In this research work the use of ozone is proposed as oxidative pretreatment for gold and silver refractory ores with the aim of modifying the pyritic matrix and thus exposing the precious metals to cyanide.…”