12/27/2021 | Industrial Water Treatment | 8 MINUTE READ
Plating in Industrial Wastewater Treatment Plants
Plating is a common manufacturing process that involves placing a thin metallic layer over some type of substrate. Many manufacturers can benefit from the plating process since it provides the underlying substance with an extra layer of protection. Keep in mind that different metals provide different benefits. The types of benefits a company can obtain from performing the plating process include:
-Improved paint adhesion
-Improved corrosion resistance
Many industrial and manufacturing facilities will produce a high amount of wastewater when performing various processes like plating. This wastewater must be treated before it can be sent into the environment or reused. Without treatment, the water would cause pollution to increase. Wastewater treatment is a basic process that involves removing contaminants from water to effectively filter or purify the water.
There are many different wastewater treatment methods that an industrial or manufacturing facility can perform, which include everything from reverse osmosis to ultra-filtration. Modern plating and electroplating techniques are used across an array of industries, which include the aerospace, mechanical engineering, instrument manufacturing, and electrotechnical production industries.
Wastewater is generated from the plating process whenever the substrate parts or materials are washed. These materials are washed when applying or preparing the electroplated coatings. Before the wastewater generated from the plating process can be reused or discharged into a sewer system, it must be treated to get rid of the heavy metals and other contaminants that are found within. The following guide offers a more in-depth look at how plating wastewater can be treated.
Advantages and Drawbacks of Electroplating Wastewater Treatment
There are numerous treatments that can be used to get rid of the contaminants found in electroplating wastewater. However, each of these treatments has its pros and cons that you should be aware of. The method that works for you largely depends on the amount of wastewater that needs to be treated as well as the composition of the wastewater. There are five basic forms of electroplating wastewater that will likely need to be treated, which include:
Chrome-containing – Occurs by performing chrome plating as well as the etching of various steel parts
Cyan-containing – Develops when performing cyan copper, silver, or cadmium plating
Acidic – Occurs from the acidic zinc, copper, and nickel plating processes as well as the pickling process
Alkaline – Is generated from the decontamination process
Heavy metal salt contaminants – Occurs as a result of the surface metal treatment process
Pros of Electroplating Wastewater
The main types of treatment that can be used to get rid of the contaminants in electroplating wastewater include ion exchange, adsorption, chemical reagent, and electrochemical treatments. If you are looking to perform the most basic treatment method when attempting to remove contaminants from electroplating wastewater, you might want to use the chemical reagent method, which provides industrial and manufacturing facilities with numerous benefits.
During this treatment, the ions within heavy metals are directly converted into hydroxides via chemical reactions. The primary chemical reagents that can be used during this treatment method include lime byproducts and caustic soda. The coagulation of these hydroxides is possible when using special flocculants.
The electrochemical methods that can be used to treat electroplating wastewater will eliminate the hexavalent chrome ions in the wastewater, which will result in iron and other heavy metals dissolving. As for the ion-exchange treatment methods that are available to you, these techniques involve exchanging ions for cations and anions, which should allow the heavy metals and other contaminants to be absorbed. The main benefit of using this method is that your consumption of freshwater will be effectively reduced by as much as 2-4x when compared to other treatment methods.
Cons of Electroplating Wastewater
While each of the aforementioned treatments can benefit you and your facility, there are also some drawbacks that you should be aware of and take into account before making your final decision. For instance, the chemical reagent technique is a relatively slow process, may not be as effective as you anticipated, and has a relatively high reagent consumption.
As for the electrochemical treatments, these treatments are relatively complex and can take a long time to be completed depending on the pH of the specific media that you use as well as the intensity of the treatment. Even though ion-exchange treatments are effective at reducing heavy metal contaminants, the reagent that you will be tasked with using is excessive. Your facility will also use a substantial amount of water to wash the ion materials. Equipment costs can be high as well, which you will need to factor into your wastewater treatment budget.
The adsorption process that typically occurs as the final stage of the electroplating wastewater treatment process is able to get rid of any metals that remain in the water after the previous treatments. However, the limitations and downsides of this process include high reagent consumption, the need for bulky equipment, and high sorbent costs.
Characteristics of the Electroplating Industry
The plating industry began for the purpose of applying chemical and mechanical coatings to different materials in order to improve corrosion resistance, wear resistance, hardness, and decorative properties. It’s possible to chemically oxidize steel and aluminum, galvanize stainless steel, and anodize aluminum with this specific process, which is why it’s become a favorite throughout many industries.
As mentioned previously, wastewater is invariably generated during the electroplating process because of the need to wash parts and materials before applying the various electroplate coatings. When these parts are washed, small concentrations of heavy metals will get absorbed into the water and create wastewater. Wastewater that contains heavy metals must be treated before the water can be reused or sent into the environment. When there are too many heavy metals in the environment, they can be toxic in many ways.
Composition of Wastewater
Before you attempt to treat electroplating wastewater, it’s important to understand the composition of wastewater, which can differ depending on the type of electroplating process you use in your facility. The wastewater that is caused by the electroplating industry can be separated into concentrated solutions and washing waters, the latter of which involves diluted effluents. As for the concentrated solutions, they can include degreasing, pickling, and washing.
When heavy metals are washed away into wastewater and sent into the environment, the damage caused by these heavy metals can be extensive. Effluents that contain cyan and complex cyanide salt of various metals. Cyanide concentrations can range anywhere from 5-300mg/l. Even at levels of less than 1mg/l, cyanide can be toxic to aquatic life.
It’s also important to take a look at the damage caused by cadmium compounds. In small quantities, it’s possible for cadmium compounds to make it more difficult for fish to remain alive in their natural saltwater and freshwater habitats.
When heavy metals enter water supplies or food supplies that humans consume, a wide range of damaging health issues can develop over an extended period of time. The most severe of these health issues include heart disease, liver disease, tumors, and brain cancer. It’s because of the many problems that untreated wastewater can cause to the environment and human health that this water should be treated before further use.
Ways to Treat Wastewater from Electroplating
The purpose of treating the wastewater that’s generated from electroplating is to make sure that the heavy metal concentration within the wastewater is at allowable levels. Once you reach allowable concentrations, the water can be sent through a sewer system as purified water or can be reused for other industrial processes. Keep in mind that the treatment process will likely need to consist of multiple stages to make sure that all types of heavy metals are removed. The four steps that typically occur in the treatment process include:
Neutralization – This process involves using sodium and calcium hydroxides to neutralize the chemical composition of metals, which means that a specific pH will be set.
Flocculation – This process forms macro floccules by adding organic flocculants to the wastewater, which results in more effective treatment.
Precipitation – During this stage, any solids are separated from the water. Sludge will also be de-watered.
Polishing filtration – This form of filtration can occur with the ion-exchange method, which should result in most of the remaining heavy metals being removed.
While the aforementioned treatments are effective, a certain amount of galvanic slime will likely form during these steps. This slime can’t be taken to a landfill and will likely need to be stored on your own property in sludge storage areas.
Electroplating has proven to be a highly useful process that has many distinct applications throughout numerous industries. Whether you want to add a layer of protection to another material or improve the material’s appearance, the electroplating technique provides such benefits without too many downsides. The one issue that you should take into account is the creation of wastewater.
As you perform the electroplating process, heavy metals and other contaminants will enter the effluent. Because of how toxic high concentrations of heavy metals can be to humans as well as the environment, it’s recommended that you perform extensive treatment of this wastewater. As mentioned earlier, there are many useful treatments that you can administer when you want to get rid of the contaminants in plating wastewater, all of which should be able to provide you with the results you’re looking for.
Posted by Sensorex on December 27, 2021
Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.