6-15. Determine the lime and soda ash dose, in mg/L as CaO and Na2CO3, to soften the following water to a final hardness of 80.0 mg/L as CaCO3. The ion concentrations reported below are all mg/L as CaCO3. Assume the lime is 90 percent pure and the soda ash is 97 percent pure. Ca2+-210.0 Mg2+= 23.0 HCO=165.0 CO₂ = 5.0 Answers: Total lime addition = 118 mg/L as CaO Total soda ash addition = 31 mg/L as Na₂CO,

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