The effects of acid-precipitation and alkali-precipitation on the removal of lignin from straw alkaline pulping black liquor were compared.The flocculating effects of poly aluminium chloride (PAC) on lignin after acid-precipitation and alkali-precipitation were analyzed.The experimental results show that:Both acid-precipitation and alkali-precipitation can effectively separate lignin from the black liquor,but the removal of chroma by acid-precipitation is better than that by alkali-precipitation; When the black liquor pH is 3,the removal rates of COD and chroma are 72.0％ and 97.7％ respectively; When the black liquor pH is 13,the removal rates of COD and chroma are 55.0％ and 22.3％ respectively; The PAC has a better effect on the flocculation of lignin after acid-precipitation,and when the wastewater temperature is 55 ℃ and the PAC dosage is 45 mL/L,the removal rates of COD and chroma are 79.5％ and 98.5％ respectively; The effect of PAC on the removal of lignin after alkali-precipitation is bad.
black liquorligninacid-precipitationalkali-precipitationflocculation
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