STUDIES ON NEUTRALIZATION OF BLACK LIQUOR EFFLUENT OF PAPER MILL BY FLUE GASES

Abstract

Paper industry which to vier 150 years old in Ida, has expanded rapidly during the last two decades* Many varieties of writing, printing, packing a ni cigarette paper and straw board and mill board are inaaatactured in our c untry, :der mills consume large quantity of water and also discharge large volume of wastes. As most mills donut have adequate provision for treating e effluents, ^ a wastewaters is let ait into the river as such or often after dilution with a limited quantity of river water, which pollutes the river warm,* At a Kraft paper miii, chemical puipng is done in wbicb the raw material chips are often di ges bed, wi th chemicals Such as Sodium hydroxide or lie.. The process of pulp blowing/ Squeezing ant washing gtvee rise to dark brown coloured +cte known as block liquor (BL) which is high in pH ant COD The high pH has to be neutralized before treatment of the waste. This study alms to use flue gases produced at the mill having CO2and S02 for neutralization of the black liquor. efflu-ent of the paper rill* The flue gases are etAinduntly given + it at paper mill. By using some amount of ,ue gA s ee , not only pH neutralization will take place, little bit of air pollution will also be minimised. Flue gases containing 14$$ ar more CO2 can be easily used for neutralization of alkaline wastewaters* ' When bubbled through the weetewater, the CO2 forms carbonic acid which reacts with the base. Reaction rate is slow but sufficient if pH mad not be adjusted below 7 or 8. EI, tier bubbling ng througha perforated pipe or using spray towers is satis. factory. Carbon dioxide reacts with water to the extent of about i to form carbonic acid. In this study, flue ,gases were bubbled thrc given volume of the black liquor and for c)*nge in p value, alkalinity and colour for each set of conditions. Flue gases . n this study, were generated by putting a domes ti. e size coal furnace. To quote a typical result of the study, the pH was reduced from 12.86 to 10.16 by bubbii ng flue gas (1.5 1pm through 350 ml sample of black liquor effluent for 20 minutes at 25°C temperature and alkalinity reduced from 110680 to 9,950 mg j i as Ga CO3.