Abstract:

A new calcification process in seaweed chemical industry was studied using Ca（OH）₂ as the calcifying agent.A composite of CaCl₂ and Ca（OH）₂ was used as calcifying agent for sodium alginate instead of traditional CaCl₂ .The deter-mined double-calcium calcification process conditions were：per liter of sodium alginate glue（alginate sodium mass concen-tration was 2.5 g/L）,the adding amount of 5%（mass fraction） CaCl₂ solution was 29.0 mL,the adding amount of 5%（mass fraction） Ca（OH）₂ solution was 13.75 mL and the amount-of-substance ratio of CaCl₂ to Ca（OH）₂ in the composite calcify-ing agent was 1.19:1.Compared with the traditional process,the new calcification process did not change the yield of sodium alginate significantly,but decreased the viscosity of the obtained sodium alginate slightly from 275.1 mPa·s to 241.3 mPa·s.The adding amount of CaCl₂ was reduced by more than 40%,and the amount of total calcium ions added was reduced by 19%.The double-calcium calcification process realized the reuse of calcification wastewater,in which the mass concentration of calcium was reduced from 483 mg/L to about 20 mg/L and the electrical conductivity was reduced from 6.84 mS/cm to 4.28 mS/cm after decalcification treatment.The treated calcification wastewater reused as process water did not significantly affect the yield and viscosity of the sodium alginate product.The new process is simple in operation,not only effectively reducing the introduction of ions in the calcification wastewater,but also realizing low-cost decalcification treatment,and the decalcified wastewater would be able to be reused as process water that provides a feasible way to reduce the water consumption in the seaweed chemical industry.

Key words: seaweed chemical industry, sodium alginate, calcification process, calcification wastewater, wastewater reuse