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Wastewater collected from a local jean manufacturing plant was treated using an electrocoagulation process (EC) coupled with activated carbon (AC) adsorption. The process variables were optimized using multivariate regression coupled with nonlinear programming with nonlinear restrictions to achieve the lowest possible cost while keeping a high enough degradation rate for chemical oxygen demand (COD), color, and turbidity to fulfill the Colombian environmental regulation requirements. Under optimal conditions (pH = 5.4, s =2 mS/cm, j =14 mA/cm2, and t = 11 min) color, COD, and TOC removals of 95%, 63%, and 51%, respectively, were achieved. The biodegradability index also increased from 0.13 to 0.29, whereas toxicity tests showed a remaining toxicity of 45%. A kinetic study was conducted for the EC process. The activated carbon (AC) adsorption process was successfully used to completely remove toxicity, while further increasing color, COD, and TOC removals to 96%, 72%, and 61%, respectively. The conditions for the AC adsorption process (20 g/L of AC and 1 h) were determined by experimental adsorption isotherms and kinetic studies. The optimized EC/AC process led to an effluent satisfying the Colombian regulations and seems technologically viable with lower costs than other similar process that were reported in previous works. © 2020 Elsevier Ltd

In this work, the detailed analysis of HCN volatilization, taking place in tailing storage facilities, was made. Volatilization experiments were performed at conditions typical of gold leaching industrial tailing ponds. The meticulous statistical analysis (including full factorial 33 experimental design) let to determine the variables and their interactions affecting the percentage of HCN volatilization. Volatilization tests were performed in an open, temperature-controlled, continuously-stirred batch reactor. The percentage of HCN volatilization was directly proportional to the temperature and temperature-pH interaction and inversely proportional to the pH, cyanide concentration, and pH-pH and temperature-cyanide concentration interactions. HCN volatilization was promoted at acidic conditions. A first order rate law was used to represent the volatilization rate. The specific rate constant (k) was found to be following function of temperature and pH: k(T,pH) = Ao.exp(-18760/T), where: In(A(0)) = (0.11 +/- 0.11)-pH + (58.08 +/- 0.16). The obtained kinetic model represented properly (R-2 = 0.90) experimental data in a wide range of industrial conditions: cyanide concentration (300-2000 mg.L-1), pH (3-9), and temperature (16-20 degrees C). The increase in temperature, from 16 to 20 C, let to the increase in k, by a factor of ca. 2.5 +/- 0.8. The increase in solution pH, from 3 to 9, provoked its decrease, by a factor of ca. 1.9 +/- 0.3.

Wastewater collected from a local jean manufacturing plant was treated using an electrocoagulation process (EC) coupled with activated carbon (AC) adsorption. The process variables were optimized using multivariate regression coupled with nonlinear programming with nonlinear restrictions to achieve the lowest possible cost while keeping a high enough degradation rate for chemical oxygen demand (COD), color, and turbidity to fulfill the Colombian environmental regulation requirements. Under optimal conditions (pH = 5.4, s =2 mS/cm, j =14 mA/cm2, and t = 11 min) color, COD, and TOC removals of 95%, 63%, and 51%, respectively, were achieved. The biodegradability index also increased from 0.13 to 0.29, whereas toxicity tests showed a remaining toxicity of 45%. A kinetic study was conducted for the EC process. The activated carbon (AC) adsorption process was successfully used to completely remove toxicity, while further increasing color, COD, and TOC removals to 96%, 72%, and 61%, respectively. The conditions for the AC adsorption process (20 g/L of AC and 1 h) were determined by experimental adsorption isotherms and kinetic studies. The optimized EC/AC process led to an effluent satisfying the Colombian regulations and seems technologically viable with lower costs than other similar process that were reported in previous works. © 2020 Elsevier Ltd

In this work, the detailed analysis of HCN volatilization, taking place in tailing storage facilities, was made. Volatilization experiments were performed at conditions typical of gold leaching industrial tailing ponds. The meticulous statistical analysis (including full factorial 33 experimental design) let to determine the variables and their interactions affecting the percentage of HCN volatilization. Volatilization tests were performed in an open, temperature-controlled, continuously-stirred batch reactor. The percentage of HCN volatilization was directly proportional to the temperature and temperature-pH interaction and inversely proportional to the pH, cyanide concentration, and pH-pH and temperature-cyanide concentration interactions. HCN volatilization was promoted at acidic conditions. A first order rate law was used to represent the volatilization rate. The specific rate constant (k) was found to be following function of temperature and pH: k(T,pH) = Ao.exp(-18760/T), where: In(A(0)) = (0.11 +/- 0.11)-pH + (58.08 +/- 0.16). The obtained kinetic model represented properly (R-2 = 0.90) experimental data in a wide range of industrial conditions: cyanide concentration (300-2000 mg.L-1), pH (3-9), and temperature (16-20 degrees C). The increase in temperature, from 16 to 20 C, let to the increase in k, by a factor of ca. 2.5 +/- 0.8. The increase in solution pH, from 3 to 9, provoked its decrease, by a factor of ca. 1.9 +/- 0.3.