HEAVY METAL REMOVAL FROM EFFLUENT OF ELECTROPLATING INDUSTRY

Abstract

Efficient remediation of wastewater is essential since a large number of people worldwide are exposed to contaminated water. Water is considered to be the most crucial component of living. It was observed that in the last century, the demand for water has increased by seven times, owing to the tremendous population growth rate. Also, due to sudden growth in industrial activities, the heavy metal removal from industrial wastewater is of prime concern. Beyond a specific concentration, heavy metals and their various ionic forms pose a significant threat to the environment and human health. Heavy metals are accumulated in the environment for a longer duration than most of the other contaminants. The electroplating industry plays a vital role in the Indian economy and shall also continue to do so in the times ahead. Electroplating has become an essential process in sectors such as automotive, manufacturing, domestic appliances, and electronics. Having said the above, the development of electroplating sector brings along some negative impacts. The generation of large amounts of wastewater, especially containing heavy metals is the most adverse impact. Therefore, the study on the removal of heavy metals from electroplating wastewater is of prime importance. Chrome plating is obtained by utilizing salts of the hexavalent form of chromium (mainly CrO3). Cr(VI) and Cr(III) are the two most familiar forms of chromium having different chemical, biological as well as environmental properties. Cr(VI) is usually present in the form of thoroughly soluble and highly obnoxious chromate ions (HCrO4- or Cr2O72-), and its persistent exposure can lead to many life-threatening concerns including cancer in the digestive systems, liver damage and kidney failure, lung cancer, nervous tissue damage, skin dermatitis, severe diarrhea, and other life-threatening diseases. It is easily passable in the cell wall and can damage the cell itself. However, the trivalent form in comparison to hexavalent is stable, has low solubility and mobility, and is generally considered to be less toxic. The hexavalent form is 300 times more toxic than the trivalent. According to the EU directive, the World Health Organization (WHO) and US EPA, the maximum permissible concentration limit for total chromium has been set to be 0.05 mg/L. Attributable to its supreme toxicity, carcinogenicity, mobility, and mutagenicity, chromium is regarded as one of the most threatening heavy metals present in the world capable of posing great harm to ecological safety. Thus, eliminating hexavalent chromium (Cr(VI)) from wastewater becomes crucial for further use. A lot of efforts have been made to improve the removal efficiencies of Cr(VI), such as ion exchange, membrane separation, biodegradation, aerobic treatment, photocatalysis, solvent extraction, and adsorption. The quest for finding a suitable and robust material for environmental clean-up is a matter of prime concern. The application of an increasing number of Carbon Nanotubes (CNTs) based materials in environmental pollution management and their success stories are indicative of their capability to be used in wastewater treatment. Due to the tunable surface chemistry of CNTs, a lot of recent developments have taken place to enhance their performance in water remediation. Novel CNT composites have been synthesized by modification of surface groups of CNTs. This work is aimed at the treatment of electroplating effluent of Bharat Electronics Limited, India. The wastewater contains a considerable amount of heavy metals, especially chromium, which needs urgent attention. The easiest way to remove hexavalent chromium (Cr(VI)) is to convert it into its trivalent form (Cr(III)), which is nonhazardous. Therefore, Cr(VI) was reduced by a variety of reducing agents such as ferrous sulphate, sodium metabisulphite, and hydrazine and was precipitated using NaOH, Ca(OH)2, and mix of both. The results prove that hydrazine can almost completely remove Cr(VI) from electroplating effluent under acidic conditions. The work has been divided into five sections, namely i) Comparison between the embedded and non-embedded carboxyl group onto the Multi-walled Carbon Nanotubes (MWCNTs) for Cr(VI) removal from electroplating effluent, ii) Synthesis of iron catalyst with different percentages of iron loadings via method of impregnation and growing Carbon Nanotubes by Chemical Vapor Deposition and their sequential application in the treatment of electroplating wastewater, iii) Synthesis of nanoparticles of various metals via sol-gel auto combustion method and their resulting nanocomposites via sonication for electroplating wastewater remediation iv) Application of industrial waste (red mud) for the treatment of chromium containing industrial wastewater, and v) Comparison of several reducing agents for hexavalent chromium reduction to its trivalent form i) Comparison between the embedded and non-embedded carboxyl group onto the Multi walled Carbon Nanotubes (MWCNTs) for Cr(VI) removal from electroplating effluent: The adsorption capabilities of multi-walled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of Cr(VI) were examined as a function of several parameters namely contact time, initial pH of solution, initial concentration of Cr (VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, electrostatic interactions, and intra-particle diffusion are found to be the fundamental mechanisms describing the Cr(VI) uptake. The maximum uptake of Cr(VI) ion by raw MWCNTs as well as MWCNTs with embedded carboxyl group were found to be 84.75 and 78.13 mg/g, respectively, as evaluated by the Langmuir adsorption isotherm model. This is with regard to the electron-rich atoms inside the functional group, which repels the dichromate anions. The kinetic parameters and equilibrium models were solved via nonlinear regression using GRG solver. The quality of the fit was verified by the coefficient of determination (R2), and the average relative error (ARE), and pseudo-second-order fitted well with the data. ii) Synthesis of the iron catalyst with different percentages of iron loadings via method of impregnation and growing Carbon Nanotubes by Chemical Vapor Deposition and their sequential application in electroplating wastewater treatment: Iron catalyst supported over Magnesium Oxide had been synthesized with varying percentages of Fe, i.e., 0.5%, 1%, 5% by employing the method of impregnation. These synthesized Fe/MgO catalysts were used to grow the Carbon Nanotubes (CNTs) using a Chemical Vapor Deposition (CVD) method. The 5% Fe/MgO catalyst showed the maximum growth of CNTs. The synthesized 5Fe-CNTs were investigated for their adsorption capabilities for the removal of hexavalent chromium from electroplating effluent. The 5Fe-CNTs were characterized by various techniques such as Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA) and Zeta analyzer. The synthesized 5Fe-CNTs showed a superior adsorption capacity of 61.34 mg/g towards Cr(VI) in wastewater. Several process parameters for Cr(VI) elimination from wastewater have been optimized. The kinetic parameters and equilibrium models were solved via nonlinear regression using GRG solver. The quality of the fit was verified by the coefficient of determination (R2) and the average relative error (ARE), and it was observed that the experimental data is in best agreement with pseudo-second-order kinetics. Furthermore, the synthesized CNTs exhibited excellent reusability. Even after 3 repetitive adsorption-desorption cycles, the efficiency of synthesized CNTs was reduced by less than 10%. iii) Synthesis of nanoparticles of various metals via sol-gel auto combustion method and their resulting nanocomposites via sonication for the treatment of electroplating wastewater: Magnetic magnesium ferrite nanoparticles (MgFe2O4), Cobalt Ferrite nanoparticles (CoFe2O4), and Nickel ferrite nanoparticles (NiFe2O4) were synthesized by employing the sol-gel method. These nanoparticles were ultrasonically decorated onto the Multi-Walled Carbon Nanotubes (MWCNTs) to produce corresponding magnetic nanocomposites. The as-prepared materials were investigated for their capability to treat wastewater loaded with heavy metals. The synthesized nanocomposites were characterized by Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Fourier Transmission Infrared Spectroscopy (FT-IR), Raman Spectroscopy, Thermogravimetric Analysis (TGA), and Zeta Analyzer. Besides, the effect of the environmental chemistry of the solution was determined by varying the critical parameters. The kinetic parameters and equilibrium models were solved via nonlinear regression using GRG solver. The quality of the fit was verified by the coefficient of determination (R2) and the average relative error (ARE). The adsorption isotherm of Cr(VI) adsorption onto the as synthesized magnetic magnesium ferrite nanocomposite (MMFNC) best fitted the Langmuir Adsorption Isotherm model. The high adsorption capacity of 175.43 mg/g was achieved at a temperature of 40°C under optimized conditions. Due to the magnetic nature of MMFNC, they are easily recoverable from the aqueous solution making them cost-friendly. Even after seven consecutive adsorption-desorption cycles, the MMFNC presented an efficiency loss of less than 20% for the removal of Cr(VI) ions. The adsorption isotherm of Cr(VI) adsorption onto the as-synthesized CoFe2O4/SM-MWCNTs best fitted the Langmuir Adsorption Isotherm model. The high adsorption capacity of 100 mg/g was achieved at a temperature of 40°C under optimized conditions. Besides, the magnetic properties of synthesized CoFe2O4/SM-MWCNTs nanocomposites allow them to separate from the aqueous solution by magnetization easily. Even after seven consecutive adsorption-desorption cycles, the CoFe2O4/SM-MWCNTs nanocomposites presented an efficiency loss of less than 20% for the removal of Cr(VI) ions. The fabricated Nickel Ferrite Nanocomposites (NFNCs) exhibited a maximum uptake for Cr(VI) of 129.83 mg/g (150 minutes) at 40°C. Besides, their inherent magnetic nature makes them easily recoverable from the solution. It was observed that even after 7 consecutive reutilization of adsorption cycles, the NFNCs presented an efficiency loss of less than 20% for the removal of dichromate ions. This study demonstrated the fabricated NFNCs as a suitable candidate for environmental remediation. The presented development method offers prospects in developing a highly effective magnetic adsorbent for heavy metal removal from wastewater. iv) Application of real industrial waste (red mud) for treatment of electroplating effluent: In this work, industrial aluminum waste, Red Mud, has been activated to check its potential in the vi management of electroplating wastewater containing hexavalent chromium ((Cr(VI)). A comparison between the adsorption capabilities of red mud (RM) and activated red mud (ARM) towards Cr(VI) from electroplating wastewater has been made. The effect of several process parameters has been evaluated. The adsorbents were characterized by various characterization techniques such as Field Emission Scanning Electron Microscopy (FESEM), Fourier Transmission Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Zeta potential, and Thermo-Gravimetric analysis (TGA). The particle size was observed to 23.59 nm. The ARM demonstrated a good uptake of 25.641 mg/g at a pH of 2, adsorbent dosage of 2g/L, initial concentration of Cr(VI) of 100 mg/L, and at room temperature. The kinetic parameters and equilibrium models were solved via nonlinear regression using GRG solver. The quality of the fit was verified by the coefficient of determination (R2) and the average relative error (ARE). The Langmuir equilibrium isotherm fits best with the isotherm data. The kinetic study has been performed to verify that the pseudo-second-order fits best with the data. Besides, the ARM showed decent reusability. The Cr(VI) removal efficiency of ARM was reduced by around 30% even after 3 repetitive adsorption-desorption cycles. The results recommend ARM to be an efficient and cost-effective material for Cr(VI) removal from industrial wastewater. v) Comparison of several reducing agents for reduction of hexavalent chromium to its trivalent form: The easiest way to deal with Cr(VI) is to reduce it into its trivalent form. Exhaustive chemical analysis was done to reduce Cr(VI) by using sodium metabisulphite (Na2S2O5) and ferrous sulphate (FeSO4). And after the reduction process, precipitating agents such as (Ca(OH)2), (NaOH) and a combination of the two were used to precipitate Cr(III) as hydroxides. Various parameters were varied and optimized. It was observed that the % Cr(VI) reduction increased from 88% to 99.97% when the dosage of sodium metabisulphite risen from 40 mg/L to 100 mg/L at a pH of 2. The highest removal of 98.2% was obtained by using the combination of Ca(OH)2 and NaOH at a pH of 9. The reduction of Cr(VI) using hydrazine was also studied. The effect of several parameters, especially molar ratios of Cr(VI) to N2H4, reaction temperature, and pH on the reduction kinetics, was evaluated. Experiments indicate that the overall reaction was the third order. In addition to the overall order, it was also observed that it is first-order with N2H4 and second-order with hexavalent chromium. The maximum percent reduction was found to be 91.6%, 95%, and 96.8% for the molar ratio of 1:5 for 25°C, 35°C and 50°C respectively. The empirical activation energy of the reaction was calculated to be around 35.22 kJ/mol. The sludge generated was characterized using techniques such as FTIR, XRD, and FESEM.