ULTRASOUND ASSISTED OXONE ACTIVATION BY NANO ZERO VALENT IRON FOR REMEDIATION OF CYANIDE AND TOTAL PETROLEUM HYDROCARBONS IN INDUSTRIAL WASTEWATER

Abstract

Aqueous free cyanide is defined as the sum of the cyanide present as either hydrogen cyanide (HCN) or its deprotonated form, the cyanide anion (CN-), and is regarded as most acute toxic kind. Cyanide, as a chemical compound, can be found in the effluents of numerous industries, particularly mining, and refinery operations. The toxicity and concentration control of cyanide during industrial process and precious metal extractions necessitate the precise detection, determination and treatment of this compound. Therefore, this topic has been of prime focus for control and treatment of cyanide wastewater matrices. In the theoretical part, numerous cyanide treatments have been compared and a new method of cyanide wastewater remediation via nano-zero valent iron (n-ZVI) and Oxone is proposed along with their chemistry and working mechanism. Later, the system thermodynamics, cyanide speciation with nZVI and free cyanide analysis technique as per developed standards is also discussed. In the experimental part, two set of water matrices (i.e. cyanide in DI water and polluted water) have been treated, analyzed and compared. Refinery tailings from a confidential company in South Korea with a free cyanide concentration of 12 ppm has been analyzed and investigated in this study. The current methodology being used at refinery complex to destroy cyanide is by means of alkaline chlorination, in which cyanide is converted into cyanate and is further oxidized into carbon dioxide and nitrogen. This tiresome process in terms of process economics, stringent process variables (such as pH) and low selectivity for cyanide among other hydrocarbon species is however replaceable. Since cyanide possesses extremely high affinity for metals thus nZVI was employed for the cyanide removal. The nZVI is corroded under sonication conditions in the presence of Oxone and yields ferrous ions (Fe+2). These ferrous ions (Fe+2) makes an insoluble ferro-cyano complex as soon as they encounter free cyanide. Best results have been obtained at a nZVI catalyst loading of 0.3 mg/l and slightly lower pH (5.5 to 6.5). And a cyanide removal efficiency of 99% from refinery tailings has been successfully achieved.