Electroplating is a versatile deposition process in which thin layers of metals and metallic alloys are deposited on a substrate for aesthetic, rust prevention, and wear resistance purposes. The electroplating business produces a variety of wastes that are dangerous to human health and the environment. Wastewater, waste solvent, spent process solutions, and sludge is the most common waste streams created in electroplating operations, thus leading to electroplating pollution.
Heavy metal ions, such as nickel, chromium, zinc, lead, silver, cadmium, mercury, and cyanides, are more dangerous in the trash. Hazardous waste created by the electroplating business is a serious environmental concern. To avoid contamination, it is essential to manage the waste created by the electroplating sector.
Different types of electroplating waste
Electroplating is a significant source of pollution because it produces hazardous wastes in toxic chemicals and heavy metals released into the environment via wastewater, air emissions, and solid wastes [8,9]. The Hazardous Waste (Management and Handling) Rules of 2002 identify the following wastes from the electroplating industry:
- Acid Residues
- Residue of Alkali
- Rinse the water used in the pre-treatment and plating processes.
- Cyanide and hazardous metals in a spent bath
- Sludge from an organic solvent-containing bath
- Sludge containing phosphate
- Remains of etching
- Metal sludge plating
- Wastewater treatment sludge (chemical sludge).
The majority of the waste created during the electroplating process is in liquid form. The pollution produced by them is more hazardous than pollution caused by solids and gaseous discharge, and it has had a significant impact on public health. Heavy metal ions, such as nickel, chromium, zinc, lead, silver, cadmium, mercury, and cyanides, are more dangerous in the trash.
The concentration of waste is determined by the surface area and form of the article, the thickness of the solution, the rate of removal, and the draining time, among other factors. Cleaning acids, alkaline cleansers, and other wastes are the most important components of these wastes. Bottom sludge including chromium, ferric, sulphate ions, and metallic contaminants are hazardous solid wastes. Gaseous emission occurs during the electroplating process due to the plating bath’s high temperature or extreme agitation. It comprises volatile organic compounds, chlorinated solvent vapours, and metals such as Platinum, Hexavalent Chromium, Rhodium, Cadmium, and others, vapours of electroplating chemicals, and cyanide vapours from the plating bath.
How electroplating pollution affects the environment?
Electroplating is a very beneficial technique used for anti-corrosion, heat resistance, electrical conductivity, and aesthetic reasons; however, it is a significant source of pollution in the environment despite these advantages.
The electroplating business produces a lot of effluents that contain a lot of heavy metals. In nature, heavy metals can be dangerous depending on their concentration. Toxic pollutants from the electroplating industry, including cyanide, cadmium, mercury, chromium, and arsenic, are often dumped into lakes and rivers, contaminating the water and posing significant health risks to humans. Water containing heavy metals has an impact on soil quality as well. A substantial portion of metals that reach the soil surface is firmly linked to colloidal components.
As a result, appreciable quantities of metals might be mobilised over time, either owing to the breakdown of soil organic matter or due to soil caused by internal soil processes or due to acid depositions, increasing the mobile metal concentration. The mobilisation of metals is caused by changes in soil characteristics such as a reduction in pH, a change in redox potential, increased decomposition of organic matter, and the loss of fine-grained particles from the soil. The solvents and vapours used in hot plating baths produce high amounts of volatile organic compounds, volatile metal compounds, and hydrogen cyanide gas.
Hazardous wastes produced by electroplating businesses are a serious environmental concern. To avoid contamination, it is important to manage the waste created by the electroplating sector. Various strategies for waste control have been developed in this context. One of the most effective techniques for reducing produced trash at the source is waste minimisation. This may be accomplished through modifying processes and improving operations.
Controlling electroplating pollution
Many businesses create excessive waste as a result of poor electroplating processes, and disposal becomes a major issue. The goal of a waste minimisation procedure is to decrease the number of byproducts dumped as waste and harm the environment and guarantee that this formation is kept to a minimum. Because hazardous waste treatment is complex and expensive, the practice of waste reduction becomes even more important when the trash generated is of a “hazardous” type. Five fundamental steps make up an excellent waste minimisation strategy:
- By exchanging less dangerous chemicals with more hazardous chemicals, it is feasible to reduce hazardous waste. Cyanide, for example, is one of the most dangerous toxic wastes generated in the metal finishing industry. Because of its chelating characteristics, cyanide is employed as a solubility enhancer, and cyanide-based solutions have better ‘throwing power.’ The plated component will have a smoother and brighter finish as a result of this. At a macro level, the disadvantage of utilising acid-based baths can be mitigated by carefully racking the workpiece inside the plating bath to ensure uniform current distribution. Non-cyanide chemicals, on the other hand, need a more thorough cleaning of surfaces to achieve high-quality finishing and hence necessitate high-quality degreasing procedures. It’s also possible to replace cadmium-based plating solutions with materials like zinc, titanium dioxide, and aluminium. It is also possible to replace the highly hazardous hexavalent chromium with the less toxic trivalent chromium, which utilises far lower quantities of chromium metal and generates less dangerous air emissions. For decorative chrome applications, trivalent chromium might be a good substitute.
- Housekeeping might be improved to reduce waste volume and strength by:
- changing the washing process, for example, by utilising countercurrent washing, lowering cleaning frequency, and reusing the spent solvent; and
- developing innovative cleaning procedures for production lines; and
- altering the trash transportation technique; and
- Cleaning the metal components with biological degreasing Water as an alternative or a soap water solution that may be recycled and used for gardening.
- The baths’ solutions might be recycled or repurposed. The following are three processes that might be useful in this situation:
- Regeneration of acid solutions: Distillation, acid absorption, membrane electrolysis, crystallisation, and diffusion dialysis are all used to renew acid solutions in this procedure. Diffusion dialysis works by moving water through the waste acid stream in a countercurrent flow. Anions and hydrogen will diffuse through the membrane into the water when the two streams meet at a membrane. Operators will finish up with an acid solution at around the same concentration as when they started and a diluted acid waste containing the metal component.
- Used alkaline and acid cleansers from the cleaning procedure are two of the most typical instances of this method. The acid dip rinse water is piped to the alkaline cleaning procedure and used as rinse water. If the flow rates for the acid dip and alkaline cleaning processes are the same, this approach saves 50% on water.
- Spent solution bath reuse: Dumping process baths that have grown too polluted to be utilised for plating is a regular occurrence. On the other hand, such baths can be useful in other metal finishing procedures such as chrome treatment, cyanide treatment, and metal precipitation and should not be discarded. This repurposing will help cut down on the amount of garbage produced.
- Technological advancements may reduce waste creation. It may be accomplished through altering process technologies, as well as equipment and technology. Changing process technology is one of the most effective ways to reduce waste volume. In addition, minor modifications to the product can significantly improve operating efficiency, resulting in decreased waste creation.
- The last stage is to replace the original product with one that serves the same purpose while producing less waste. As a result, waste is reduced. For example, change non-rechargeable batteries to rechargeable batteries, use water-soluble formulations instead of volatile chemicals in spray cans, and use ammonia or other ecologically friendly ingredients in freezers instead of chlorofluorocarbons.
The metal plating business has made several environmentally friendly advancements. Waste minimisation strategies are being used to minimise the usage of cyanide, hexavalent chromium, cadmium, leads, and chlorinated solvents. Waste reduction processes are beneficial in creating an environmentally friendly industrial system with low pollution levels and implementing excellent housekeeping practices. Raw material and energy conservation has been decreased, resulting in increased financial strength for the firm. A systematic, disciplined financial management system has produced account records, inventories of raw materials, and processed items.