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Effective utilization of lime mud for the recovery of potash from mica scraps

Jena, Sandeep K., Dash, Nilima, Rath, Swagat S.
Journal of cleaner production 2019 v.231 pp. 64-76
X-ray diffraction, additives, calcite, calcium chloride, chemical analysis, feldspar, mica, muscovite, paper, pulp and paper industry, quartz, response surface methodology, roasting, scanning electron microscopy, sodium chloride, temperature, wastes
The present communication describes a novel application of lime mud, a waste material generated in paper/pulp industries, for the recovery of potash values from mica scraps. Characterization studies of the mica scraps using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) indicate the major minerals to be muscovite and quartz while the chemical analysis confirms the presence of K2O to the tune of 7.5%. Lime mud is found to be mostly consisting of calcite and quartz as the major phases. The roast-leach studies using lime mud and NaCl as the additives have been carried out using response surface methodology to optimize the factors for maximizing the potash recovery. Under optimum conditions such as a temperature of 950 °C, a roasting period of 30 min and a ratio of mica: lime mud: NaCl – 1:0.7:0.7, around 99% of the potash value could be recovered. The results, under similar roasting conditions, are found to be comparable to the ones using CaCl2 as the additive. The formation of different phases as analysed using the characterization studies suggests that the mechanism of potash extraction may follow two routes. One of them is the direct reaction of muscovite with CaCl2 (formed due to the reaction of lime mud and NaCl) to form sylvite, anorthite, and kyanite. The other one may be an indirect route in which muscovite at high temperature along with SiO2, forms K-feldspar that further reacts with CaCl2 to give the sylvite phases. It is also noticed that a further increase in roasting temperature to 1100 °C leads to a decrease in potash recovery with the possible reasons being the formation of water-insoluble K-phases like leucite as confirmed in the SEM studies.