Soda recovery from non-wood spent pulping liquor

The Indian paper industry is switching to non-wood (agro based) raw materials such as wheat straw, rice straw and bagasse instead of wood for chemical pulping due to continuing deforestation. The majority of these non-wood based paper mills are small scale and cannot afford to install a conventional chemical recovery system. Thus the discharge of spent pulping liquor to the surroundings results in high environmental impact and loss of valuable pulping chemicals. In the present study, experiments were performed to recover pulping chemical from soda-based non-wood spent pulping liquor by direct causticisation. Lignin-bound sodium was first converted to free sodium by oxidation and then subjected to direct causticisation of the oxidised black liquor.