Technical details consultation on the treatment of recycled wastewater using the lime-soda softening method
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The total hardness of the circulating wastewater is 2000 mg/L, of which calcium hardness accounts for 550 mg/L and magnesium hardness accounts for 1450 mg/L; this is permanent hardness, and the alkalinity is very low. A pilot test was conducted using the lime-soda method for water softening, but the results were very unsatisfactory; the total hardness was reduced only to 1500 mg/L. During the experiment, Ca(OH)2 was first added at a concentration of 1.2 g/L, followed by Na2CO3 at a concentration of 2.2 g/L. I’m not sure what the problem is; I hope some experts in this field can offer some guidance. Thank you in advance!
This post was last edited by yuchenchf on 2018-4-2 at 16:05. It is recommended to apply a film directly. The concentrated high-hardness wastewater is then softened using the lime-soda method; the higher the concentration, the better the softening effect.
(1) Lime dosage: CaO = 28/ε1(CO2 + A0 + HMg + α), mg/L. (2) Soda ash dosage: Na2CO3 = 53/ε2(HY + β), mg/L; 228.70 = 286.76. A0: Total alkalinity of raw water (based on H+), mmol/L； HMg: Raw water magnesium hardness (calculated as 1/2 Mg2+) (mmol/L) ； HY: Permanent hardness of raw water (calculated as 1/2Ca2++1/2Mg2+) (mmol/L) ； Na2CO3: amount of soda ash added (mg/L) ； β: Excess amount of soda ash (calculated as 1/2Na2CO3) (mmol/L); generally, it ranges from 1.0 to 1.4 mmol/L. 53: Molar mass of 1/2Na2CO3 (mg/mmol) ； ε1: Purity of quicklime (%)) ； ε2: Purity of industrial soda ash (%)) ；