Recovery of Ni from Ni-bearing Wastewater by Coprecipitation with Iron (Fe)
Introduction
Ni is an essential trace element that plays a vital role in many natural and industrial processes, such as catalytic reactions, metallurgical processes, and even construction materials. It can be harmful when in high concentrations due to nickel-bearing wastewater released into surface waters and groundwater sources. Therefore, it is particularly important to develop effective techniques for recovery of Ni from wastewater. One method for the recovery of Ni from wastewater is coprecipitation with iron (Fe).
Process Description
Coprecipitation of Ni with Fe is a process by which insoluble metal hydroxides are formed, with the solubility of Ni(OH)2 lower than that of Fe(OH)2. This process is based on the acid-base behavior of components like Ni and Fe, which precipitate from solution when the concentration of hydroxide ions from neutralization of acidic species increase. To initiate this process, the basicity of the solution must first be adjusted. This can be accomplished by the addition of a base, such as lime, to raise the pH of the solution.
Once the pH of the wastewater is completely adjusted, Fe-containing materials like steel scrap, slag, or iron powder can be added in a controlled amount to ensure complete precipitation of Ni. Upon mixing, a solid precipitate is formed due to the reaction between the Ni and Fe, resulting in the recovery of Ni from the solution. Next, the solidNi-Fe precipitate is settled by gravity and then filtered to separate it from the wastewater. Finally, the recovered Ni can be extracted for further uses.
Advantages
One of the main advantages of applying this coprecipitation technique is that, unlike other recovery processes, it does not require the use of expensive chemicals or equipment. Furthermore, because it is a relatively simple process, it can easily be scaled up for larger wastewater treatment needs. Additionally, the ability to select specific Fe-containing materials makes it cost-effective, since it allows for the use of inexpensive secondary materials, such as steel scrap or slag. This also has the additional benefit of making the process more environmentally friendly by avoiding the release of additional contaminants in the aquatic environment.
Disadvantages
There are some disadvantages to the coprecipitation technique, however. First, a certain amount of Fe is required to precipitate the Ni, which can be a challenge to obtain or produce in larger amounts. In addition, the process is limited to treating wastewater with relatively low concentrations of Ni, and it cannot be used for high concentrations of Ni in more acidic conditions.
Conclusion
The coprecipitation technique for Ni recovery from Ni-bearing wastewater is a promising approach for large-scale wastewater treatment. This process does not require the use of any expensive chemicals or equipment, and it is simple enough to adjust to any wastewater treatment situation. Additionally, the process allows for the use of inexpensive secondary materials, making it cost-effective and environmentally friendly. However, the process can be limited in treating wastewater with higher Ni concentrations and/or more acidic conditions. In general, this process is a reliable and effective tool for recovery of Ni from industrial wastewater, and is likely to become more widely used in the future.
