Reducing and Oxidizing Agents

Reducing agents donate electrons while oxidizing agents accept electrons, critical in bleaching, stripping, discharge printing, and vat dyeing. Reducing agents include sodium hydrosulfite (2-10 g/L, most common, used in vat dyeing, discharge printing, stripping, bleach cleanup, COD contributor, $1.50-3/kg), thiourea dioxide (0.5-2 g/L, stable, less odor, discharge and reduction clearing, $4-8/kg), glucose-based systems (eco-friendly, traditional indigo dyeing), and ascorbic acid (mild, safe, wool bleaching, expensive $8-20/kg). Oxidizing agents include hydrogen peroxide (2-10 g/L H2O2, dominant bleach, cotton 5-10 g/L at 90-100°C achieving whiteness 75-85, degradation product H2O + O2 environmentally benign, $0.50-1.50/kg), sodium hypochlorite (2-5 g/L available Cl, powerful but declining due to fiber damage and environmental concerns, $0.30-0.80/kg), sodium chlorite (pH 3.5-4.5, most powerful whiteness 85-90, toxic ClO2 gas, declining use, $2-5/kg), peracetic acid (5-15% solutions, faster than peroxide at 50-70°C, antimicrobial, $3-8/kg), and potassium permanganate (discharge printing, limited use, $4-10/kg). Stabilizers for peroxide include sodium silicate (1-3 g/L), phosphonates (0.2-1 g/L), and magnesium salts (0.5-2 g/L). Applications span bleaching, vat dyeing, discharge printing, stripping, and reduction clearing with environmental concerns about dithionite COD and chlorine AOX driving peroxide preference and catalytic bleaching development.