Lead and Zinc Smelting Wastewater Treatment
Introduction
Lead and zinc production involves a variety of processes that yield heavy metal-containing byproducts and waste streams, such as priming and smelting of ores, resulting in acid drainage water and slag requiring treatment and disposal. The efficient and timely removal of dissolved heavy metals and suspended solid matter is particularly important as heavy metals are toxic, even in trace quantities, and disposing of large quantities of these elements may cause long-term environmental damage.
Lead and zinc smelting wastewater contains large amounts of dissolved heavy metals and suspended solids and needs thorough treatment. Generally, the wastewater needs pre-treatment followed by biological treatment to remove the pollutants.
Chemical processes
Chemical treatment of lead and zinc smelting wastewater involves chemical precipitation, flocculation, filtering and membrane filtration.
Precipitation is a process of adding a chemical reagent like lime to neutralize the acidic water and to precipitate the heavy metals in solution. The sludge formed is collected and disposed.
Flocculation is done to increase the settling rate of suspended solids, which involves adding a flocculant like polyelectrolyte at concentrations of 0.2-0.5%. The flocculant forms large particles around the suspended solids and these settle faster than the small particles, thereby making them easier to remove from the water.
Filtration involves passing the wastewater through a series of filters to remove any remaining suspended solids. These filters can be of various types like sand, activated carbon, etc. The filters need to be backwashed regularly to prevent any clogging.
Membrane filtration is done to remove dissolved impurities and suspended solids from wastewater. In this process, wastewater is forced through a membrane filter which acts as a barrier, allowing only clean water to pass through while trapping any remaining impurities.
Biological processes
Biological treatment of lead and zinc smelting wastewater involves aerobic and anaerobic treatment.
Aerobic treatment involves introducing oxygen in the wastewater and allowing aerobic organisms to break down the organic matter in the wastewater. The process is efficient in removing biochemical oxygen demand (BOD) and suspended solids from the wastewater.
Anaerobic treatment involves introducing anaerobic organisms to break down the organic matter in the wastewater. This process is effective in removing BOD and reducing sludge volume.
Conclusion
Lead and zinc smelting wastewater needs to be treated to remove the pollutants it contains. The treatment process involves both chemical and biological processes. Chemical processes such as precipitation, flocculation, filtration and membrane filtration are used to remove solids and heavy metal from the wastewater. Biological processes like aerobic and anaerobic treatment are used to break down the organic matter in the wastewater. Treatment of lead and zinc smelting wastewater is necessary to prevent pollution of the environment.
