Study on Ca–Al synergy promoting desilication and sedimentation in alkali recovery green liquor of bamboo pulping

Abstract High silica in non-wood fibers (wheat straw, bamboo, reed, bagasse, etc.) restricts their pulping and papermaking application, lacking feasible solving methods. This study adopted nano-calcium carbonate (NCC) combined with Al 2 (SO 4 ) 3 for green liquor desilication. Results indicated desilication efficiency rose notably with increasing Al 2 (SO 4 ) 3 dosage. When Al 2 (SO 4 ) 3 dosage increased from 20 mol% to 100 mol% (based on Si molar content in green liquor), the desilication rate grew from 42.72 % to 92.61 %. However, the single Al 2 (SO 4 ) 3 system caused poor sedimentation (30 min standing sedimentation height: 208 mL) and reduced green liquor pH from 13.63 to 12.26. NCC acted as crystal nucleus to induce silica precipitation growth, greatly enhancing settling performance. Under optimal conditions (10 % NCC dosage, 20 min dispersion, 100 mol% Al 2 (SO 4 ) 3 , 5 min reaction), the desilication rate remained 92.61 %, and sedimentation height dropped sharply to 38 mL. The composite technology realized rapid silica removal and settlement, with high retention of NaOH. The overall process flow was shown in Figure 1.