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Characterizations of Lime Sludge from Indian Paper Industry: A Step towards Sustainable Growth for Indian Cement Industry

The kraft process of wood into wood pulp in the paper and pulp industry in the chemical recovery section generates lime sludge (LS) through the burning of the lime kiln. This by-product lime sludge from the paper industry has the major chemical composition of calcium carbonate in the form of calcite, moisture and minors are silica, magnesium, iron and aluminium. Here, we characterized the collected industrial lime sludge by-product from different parts of the country and evaluated its potential application in engineering construction material. The chemical composition of all samples contains CaO in around (52-55) %, SiO2 (1-4) %, Al2O3 and Fe2O3 make up less than 1% by weight. Minor alkalis of Na2O, K2O and SO3 content are less than 1 wt%. XRD profile and TG/DTA results showed that all lime sludge samples have major calcite (CaCO3) phase. The particle size distribution showed that grains are in the range of 11μm to 23μm which is compatible for cement manufacture and construction. Investigation by optical microscopy of microstructure and morphology revealed that calcite grains are presents as rounded shape agglomerated form. The characterization of all obtained results are encouraging for replacement of limestone in the cement and construction industry by using lime sludge which is technically suitable and economically viable for waste management in favour of circular economy.