Sewage treatment from heavy metal ions by the method of deposition, using sulfur-alkaline wastewater as a reagent

Abstract

Aim: Wastewater, containing heavy metal ions (HMI), is formed at the metal mining, working, and manufacturing enterprises. If wastewater is not effectively treated, these contaminants enter the environment, accumulate in animals and plants, and enter the human food chain, leading to disturbances in the normal functioning of their systems and the occurrence of various chronic diseases. In this regard, wastewater treatment from HMI is an urgent task. Materials and Methods: This paper presents the research on purification of electroplating wastewater (EPWW) with sulfur-alkaline wastewater (SAWW), containing sodium sulfide, which is a reagent for the removal of HMI by the method of precipitation. Result and Discussion: It was found, that when mixing of EPWW and SAWW, dark brown sludge was formed immediately. The performed X-ray structural analysis of sludge allowed to establish, that crystals of chalcopyrite (СuFeS2) (46%), aluminum tri-nickel (ÐlNi3) (28%), and copper (II) oxide (26%) were present in its composition. Investigation of the mass of the formed sludge from the ratio of volumes of mixed EPWW and SAWW allowed to determine experimentally their optimum volume ratio, equal to 50:1, respectively. Investigation of the kinetics of sedimentation showed the possibility of applying the method of precipitation, using standard equipment for separation of sediment from the water part. It is shown, that the concentration of HMI in the treated wastewater is below the maximum permissible values of the standard indicators, established for centralized water disposal systems. Spectrophotometric method was used for the determining of iron and nickel ions in purified water; the method of stripping voltammetry was applied for revealing the ions of zinc and copper. It has been found, that when mixing wastewater, there was an increase in the values of chemical oxygen demand, which could be reduced to the discharge norms for biological waste treatment facilities (500 mg О2/l), when treating mixed water with ozone-air mixture or air oxygen for 5 and 40 min, respectively. Conclusion: The analysis of the results of conducted studies showed the efficiency of purification of EPWW by the method of precipitation, using as a reagent the waste product - SAWW below the established standard indices, without the use of expensive alkaline reagents and sodium sulfide