Beneficiation of limestone plant rejects for value addition.

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 for treating this sample. A process flowsheet was developed to treat these rejects based on the studies carried out. This process can minimize the waste generation and the concentrate generated during this process can be directly utilized in the Indian cement industries.

An assessment of heavy metal contamination in soils of fresh water aquifer system and evaluation of eco-toxicity by lithogenic implications.

The chemistry of heavy metals in sediments with respect to bio-availability and chemical reactivity is regulated by pH, texture, and organic matter contents of the sediments and specific binding form and coupled reactivity of the metals within. To focus on the metal distribution (Fe, Mn, Pb, Cd, Zn, Co, Cu, and Cr) and behavior in a fresh water aquifer system along with the ecological toxicity parameters, a four-step sequential extraction method was applied on 18 Eastern Ghats' type sediments from fluorosis-hit Nayagarh district, India. Geo-accumulation index of metals in the sediments indicates that they are practically uncontaminated and/or less contaminated with and Fe, Mn, and Cu; contaminated to moderately contaminated with Pb, Zn, and Cr; and strongly contaminated with Cd. Rather, more than 80 % recovered Cd metal concentration in sediments constitute the labile fractions. Temporal clustering of metal fractions indicates transition metal fraction distribution claiming the sediment pH regulation. Similarly, base metal distribution accounts for organic carbon and soil conductivity due to their greater availability in exchangeable and sulfide fractions. Correlation analysis and factor analysis scores demonstrate lack of inter-relationship between transition group and base metal fractions. High fluoride concentration in ground water is associated with high sodium-bicarbonate-iron affinity with elevated pH values (i.e., >7.0) and high positive factor score with the total iron concentration in ground water.