What is the minimum hardness that can be produced using the lime soda ash process?

The minimum hardness that can be produced using the lime soda ash process is indeed 25 mg/L. This process is designed to remove hardness from water by utilizing lime (calcium hydroxide) and soda ash (sodium carbonate) in a treatment process that precipitates calcium and magnesium ions, which are major contributors to hardness.

During this process, lime is added to raise the pH of the water, which facilitates the conversion of soluble calcium and magnesium salts into insoluble precipitates. Soda ash is then added to further enhance the precipitation of these hardness-causing minerals. The result is softened water with a manageable level of hardness remaining.

The choice of 25 mg/L reflects the practical consideration that this is the minimum level of hardness that can be achieved while still maintaining sufficient mineral content for water quality standards and for various uses of the treated water. This level is typically deemed acceptable for many applications, including industrial processes and dilution in potable water supplies.

Higher values like 50 mg/L or 75 mg/L, while they are feasible in some treatment scenarios, do not represent the effective lower limit achievable through the lime soda ash method, which focuses specifically on balancing hardness reduction while maintaining water quality.