Item Superfine Grade First grade Qualified grade Purity≥ 99.5% 99.0% 98.0% Moisture≤ 0.30% 0.50% 0.80% Water insoluble substances≤ 0.01% 0.03% 0.03% Sulfate(SO4)≤ 0.01% 0.02% 0.02% Fe≤ 0.005% 0.03% 0.05% Cl≤ 0.15% 0.20% 0.30%