Semiconductor wastewaters are inherently difficult to treat. They are usually characterized by strong color, high chemical oxygen demand (COD), high levels of volatile organic compounds (VOC) and heavy metals, resulting in potential contamination of the environment. Conventionally, chemical coagulation and biological treatment are used to treat wastewater before discharge.
The industrial standard method for removing contaminating metal ions from a wastewater stream is by raising the pH to a level that causes the formation of insoluble metal hydroxide precipitates.
Besides is a graph showing the solubility of common heavy metal ions versus pH.
This can be complex and dangerous process. As we can see in the graph some metal ions need the pH adjusted to fairly high pH’s to achieve the formation of insoluble metal hydroxide precipitates.
More alkalinity than caustic soda
When an alkaline compound dissolves in water, it produces hydroxide ions, OH–. These ions are responsible for the alkalinity of the solution.
Because magnesium hydroxide (Mg(OH)2) provides two (2) hydroxides for alkalinity compared to one (1) with NaOH (caustic soda), the usage rate for Mg(OH)2 is much less than that required for NaOH.
Lower cost-per-pound ≠ cheaper
While AMALGAM-60 is typically more expensive then 50% NaOH on a “price per unit” basis, it is significantly less expensive in use – because every 1.0 lb of 50% NaOH can be replaced by 0.6 lbs of 60% Mg(OH)2 to provide the same number of moles of hydroxide (OH–) for pH neutralization.
Magnesium hydroxide unequally aids metal ion precipitation.
Magnesium Hydroxide provides two different pH environments within the same solution matrix. Most obviously, as Mg(OH)2 dissolves in water it releases free hydroxide ions (OH–) that neutralize any acidity in the water, driving an increase in the bulk water pH.
Less obviously, any micron-sized particles of Mg(OH)2 that have yet to dissolve possess a pH within their micro-environment that will be in the range of 9 to 11, providing a nucleation site for those metal ions that form insoluble hydroxides at higher pH values.
Safer and greener means more savings
Unlike caustic soda, AMALGAM is non-hazardous and non-corrosive, which makes it easier and safer to handle. Spill is not reportable.
Because magnesium is a macronutrient – it is the core element of chlorophyll (makes everything green!) – it is also beneficial to the environment while sodium is a salinity hazard.
Magnesium also has coagulation properties that sodium does not. This can result in reduced sludge volume and reduced sludge hauling fees.
IER is a supplier of environmentally friendly water and wastewater treatment chemicals and equipment.
IER offers Magnesium Hydroxide-based products as safe, earth-friendly alternatives to the use of caustic soda for pH neutralization, along with proprietary polymer solids removal technologies.
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