Beneficiation of limestone plant rejects for value addition

Attempts have been made to recover the additional calcium values from the limestone plant rejects by flotation as a beneficiation technique. The characterization study indicates, quartz and calcite are the major minerals present in this sample, while concentrate is highly upgraded with calcite content, by rejecting mostly quartz and clays in the tailing. Systematic studies have been conducted at different operating conditions using conventional cell and column flotation. A concentrate of 42.50% CaO content at an yield of 15.65% is produced by two stage conventional cell flotation from the limestone rejects with 12.09% CaO. Further enhancement in grade and yield of the concentrate could be achieved using single stage column flotation. The process flowsheet developed can be adopted to treat these rejects for production of cement grade concentrate. •Characterization study was conducted to confirm the mineral phases and their relative distribution in the studied sample.•Two stage conventional cell flotation studies were carried out to beneficiate the limestone plant rejects.•Column flotation can be utilized for better grade and recovery of the concentrate.•The developed process can produce required grade limestone concentrate for cement industries. Investigations were carried out on lime stone rejects (−1mm) generated at a lime stone washing plant in southern India. These rejects contain 12.09% CaO, 2.95% MgO, 10.73% Al2O3, 4.99% Fe2O3, 43.05% SiO2 and 24.92% LOI. Mineralogical studies including SEM-EDAX, XRD, FTIR and TGA were conducted to confirm relative distribution of minerals in the flotation feed and products. These studies revealed that feed sample consists of quartz and calcite as the major minerals with minor amounts of montmorillonite and dolomite whereas flotation concentrate dominantly consists of calcite, and tailings mostly of quartz and montmorillonite. A commercial grade sodium silicate, oleic acid and MIBC were used as depressant, collector and frother respectively in flotation studies. The effects of different operating parameters were evaluated for both conventional and column flotation. Two stage conventional cell flotation results indicate that a cleaner concentrate of 42.50% lime (CaO) content could be obtained at a yield of 15.65%. The lime (CaO) content of the concentrate was further enhanced up to 44.23% at 20.73% yield using single stage column flotation. The column flotation is more efficient in comparison to the conventional cell f