BHANDER LIMESTONE OF BUNDI, RAJASTHANOUALITY ASSESSMENT FOR CEMENT INDUSTRY

Abstract

In the Bundi district of Rajasthan (Western India), a large tract of barren land occupied by vast surface exposures of limestone occurs conspicuously. This poorly and sparsely inhabited calcareous rock bearing terrain, with little cultivation, forms the locale of this study. This investigation aims at assessing the possible use of these limestones as raw material for manufacturing cement, the demand of which is continually increasing with the increasing developmental activities in the adjoining and nearby areas. Geographically, the area of study is located 10 km northwest-of the Bundi city along the National Highway No. 12. Geologically, these 'limestones' known as the Bhander Limestone, belong to and form a part of the uppermost unit of the Vindhyan Supergroup, (Upper Proterozoic -Lower Cambrian?). Lithologically, this area exhibits limestone along with sandstone and shales. These units have been mapped on the basis of False Colour Composite (FCC) using IRS-LISS III Satellite data and field investigations. The Great Boundary Fault, which defines the western boundary between Achaean meta-sediments and the Vindhyan Supergroup, passes just north of the area of study. The rocks in this area occur in the form of non-plunging anticlinally folded structure, with ENE-WSW axis. Pink shales forming low land occupy the core of the fold. The overlying pink to grey coloured limestone exhibits gently undulating topography and the youngest pink, pale grey, red brown to white coloured sandstone forms ridge like topographic feature. Bhander Limestone The calcareous sediments of the Bhander Limestone, locally called Lakheri Limestone, are characterized by pink, blue-grey, light grey, green and dark grey colours. Petrographic studies indicate that they are micritic in nature. Based on physical characteristics, petrography, stratification and internal structures, the Bhander limestone in this area can be classified into the following four Lithounits. Lithounit A The oldest Lithounit A consisting of pink to red coloured limestone lies over the Ganurgarh Shales (pre-Bhander Limestone) and has gradational contact with it. This argillaceous limestone is composed of micrite (as per classification of Bissell and Chilingar 1967) with 10% or more admixture of terrigenous sediments. Intramicrudite occurs in the form of lenses of flat pebble breccia. Thin sections studies under microscope show abundant horizontal fenestrae and bird's eye structures filled with sparry calcite. The features such as horizontal fenestrae, bird's eye structures, appreciable content of terrigenous admixture, general absence of algal mats, presence of micrite rich channels of small dimensions and predominant pink colour of sediments collectively indicate high to low supratidal depositional environment for Lithounit A. Lithounit B This blue to grey coloured calcareous Lithounit occurs above the Lithounit A with sharp contact. It also has in it some coarse grained beds with discontinuous lateral extent and generally devoid of sedimentary structures except for occasional symmetrical, straight crested ripple marks. These limestones show alternate dark and light coloured laminations. The calcareous beds, micritic in nature, show mud cracks suggesting their sub-aerial exposures. At places it exhibits profuse small domal stromatolites. The features such as profuse development of algal mats, mud cracks, graded bedding, high energy conditions, reversal of current direction within the channels in this Lithounit, suggest its deposition in the high intertidal flat zone and in the transitional zone onto the supratidal flat. Lithounit C Overlying the Lithounit B, this Lithounit mainly comprises fine-grained sediments in the form of calcareous shales with occasional lenses of calcareous siltstones. The shales are mostly olive coloured, but occasionally bright green. They are generally splintery in nature. The fine-grained nature of sediments together with the thin lamination and general absence of current and wave formed structures indicate suspension deposits of low energy depositional environment for this Lithounit. Lithounit D Overlying the Lithounit C, this dark grey to black coloured Lithounit 'D' is the youngest Lithounit. It consists of laminated to thin-bedded limestones, which are mainly micritic in nature. Palisade structure is common but ripple laminations, flaser bedding and symmetrical ripple marks also occur occasionally in this unit. The abundance of micrite, absence of features of intermittent exposures, black colour of sediments and presence of algal mats suggests mainly the protected, shallow, subtidal environment, in which this unit was deposited. Spectral Response of Lithounits From what has been said above, it is apparent that each Lithounit of the Bhander Limestone was born in its own depositional environment, which is characteristically indicated by the physical imprints, bio-indicators and chemical make up of sediments deposited in it. Ifthis is so, then each Lithounit should have its own spectral response to various electromagnetic waves and therefore can be differentiated from one in another. With this premise an attempt was made to identify various calcareous Lithounit of the Bhander Limestone using remote sensing data. The pixel values of IRS-LISS III data were determined for bands 2, 3, 4 and 5 in the wavelength range of 0.52 -0.59 (Green), 0.62 - 0.68 (Red), 0.77-0.86 (Near Infrared) and 1.55 - 1.70 (SWIR) respectively These Lithounits could not be differentiated in the band 2, 3 and 4. However, in Linear Contrast Image of band 5 of Short-Wave Infrared in wavelength range of 1.55 to 1.70p.m, the Lithounits A, B and D with average pixel values of 152, 140 and 127 respectively, can be identified to some extent. Bhander Limestone as Raw Material for Cement Portland cement - a commonly used binding substance is composed mainly of silicates, aluminates and ferro-aluminates of lime. Limestone is the major raw material required for the manufacturing of cement, besides other additives such as laterite, bauxite, red ochre etc. As per norms evolved by the National Council for Cement and Building Materials (India), compositionally, a limestone should have CaO between 44 and 52%, Si02 less than 14% and MgO less than 3.5% so as to qualify for use as raw material for cement manufacturing. In order to assess the quality of the Bhander Limestone for cement manufacturing, 160 representative limestone samples were collected from the area of study,covering different Lithounit. The samples were powdered to - 160 mesh size and analyzed for CaO, Si02, Al203, Fe203, MgO and Loss on Ignition (LOI), besides other minor constituents such as Na20, K20, S03, CI, P205 and Mn203. X Ray Fluorescence (XRF) technique and the Wet chemical analyses following IS- 1727-1967 and Standard method evolved by National Council for Cement and Building Materials (NCB) were carried out IV The comparison of chemical composition for various Lithounits of Bhander Limestone with the NCB prescribed specifications for cement grade limestone suggests the following: (i) The limestones of the Lithounits B and D qualify for use directly in the cement manufacturing. Lithounit D has highest CaO and lowest Si02 as compared to other Lithounits B, A and C and it therefore provides the best variety of cement grade limestone. (ii) The limestone of Lithounit Bqualifies for direct use as raw material for cement. (iii) The calcareous unit A is marginally sub-grade and can only be used, if blended with Lithounit D. (iv) The argillaceous unit- C does not qualify for cement manufacturing. In view of this, the limestone of the area has been classified into three categories - High Grade (CaO >48%, Si02 <10%), Acceptable Grade (CaO 44-48%, Si02 10-12%) and Sub Grade (CaO 42-44%, Si0213-16%). The Sub-Grade Limestone can be upgraded with the High Grade Limestone of the Lithounit D. In addition to limestone, raw materials rich in Fe203 and Al203 are also required in small quantities for the manufacturing of cement for which laterite, bauxite and red ochre are found to occur in plenty in the nearby areas namely Pratapgarh near Chittorgarh and Iswal near Udaipur, located at a distances of 220 and 280 kms. from this area respectively. Raw Mix Design for Cement Limestones, laterite / bauxite and red ochre are the important raw materials required for manufacturing cement. The proportion of each of these depending upon their chemical composition plays important role in the production of cement of desired quality. In order to optimally utilize the High Grade Limestone of Lithounit D with the Sub- Grade or blendable grade limestone of Lithounit A, several raw mix proportions were worked out along with red ochre and laterite or bauxite. Amongst the many possible proportions of these constituents, two types of Raw Mix Designs have optimally been worked out, conforming to the prescribed specifications for production of desired quality of cement, one with High Grade limestone as 12%, Sub Grade limestone as 85% laterite 2.0% and red ochre 1.0% and the other one with 12% High Grade limestone, 86% Sub Grade limestone alongwith red ochre and bauxite as 1% each. The theoretically worked out proportions were used to calculate the potential composition of kiln feed and clinker. The modulii values (ratios of oxide components in clinker) and phase compositions of resultant clinker were then calculated and compared with the standard values prescribed for cement manufacturing. The Modulii values and phase composition, thus calculated, were found to be well within the prescribed standard ranges for cement manufacturing. Laboratory Experiments Wth a view to test the efficacy of the above mentioned theoretically optimized Raw Mix Designs, laboratory experiments were conducted. The samples as per proposed designs of the two types of raw mixes were prepared from weighted average quantities of raw materials. These were ground in a ball mill to a fineness of 170 mesh size. The nodules thus prepared were fired in electric furnace at 1350°, 1400° and 1450°C temperatures. The resultant clinkers were analyzed for free lime content. The free lime content in clinker nodules based on Type 1 and Type 2 designs, were VI determined as 0.3 and 0.9% respectively and are less than maximum permissible limit of 1%, implying thereby proper burning of raw mixes. The Cement was then prepared on laboratory scale by grinding the laboratory fired nodules clinkers with 5% gypsum. The cements thus prepared for both type 1 and type 2 designs were tested for setting time, compressive strength and Le-Chatelier and autoclave expansion tests as per standard procedures. The initial and final setting time for the first and second cement samples are 55, 190 minutes and 50, 180 minutes respectively. The 28 days strength of the cements prepared was found to be 51 N/mm2 and 51.8 N/mm2 respectively, which are well above the minimum prescribed limit of 35 N/mm2. Thus these and likewise the other properties of laboratory made cement conform to Indian Standard specification for Portland cement, thereby validating theoretically worked out proportions of various constituents in both types of Raw Mix Designs. Feasibility of Setting of Cement Plant With a view to assess the feasibility of setting of a cement plant in the area, an attempt has been made to estimate the quantum of limestone, the cost of Cement manufacturing and other related expenditures. In this area, on a conservative side, the possible reserve of limestone of Lithounits A, B and D have been worked out to be of the order of 69.5, 437.5 and 96.8 million tonnes respectively. Taking 1.5 as limestone consumption factor, the calcareous Lithounits A, B and D are good enough to manufacture 403 million tonnes of cement. The cost to manufacture cement has been estimated as Rs. 1670/- per tonne at current rate. The profit margin as per current selling price of Rs 2100/- per tonne has been worked out to be Rs. 430/- per tonne. On the basis of this, it is concluded that prima facie, on techno-economic basis, an eco - friendly 2 to 3 million tonne per annum capacity cement plant can be setup in the area. The barren area with well

exposed limestone outcrops and negligible soil overburden, sparse habitation, little landuse, and availability of road and rail transport facilities, further make this limestone terrain attractive for such a venture. As a spin off advantage, the proposed cement plant can utilize the industrial wastes of lead-zinc slag of Hindustan Zinc Ltd. Chittorgarh, fly ash from the Thermal Power Plant at Kota, Phospo Gypsum from fertilizer plant at Kota and low grade gypsum from Bikaner, located at distances of 250 km, 60km, and 300 km respectively to produce Pozzolana cement and slag cement. In conclusion, it is surmised that the calcareous Lithounits B, A and D of the Bhander limestone, locally known as Lakheri Limestone, deposited in the physico chemical environment ranging from low energy to tidal (intertidal to supratidal), are quality wise and quantity wise good enough to be used as raw material for commercial manufacturing of Portland cement by an environmentally friendly cement plant in this area which is characterized by easy availability and workability of limestone, besides transport facilities. In addition, the proposed plant can also be put to use the industrial wastes of other nearby factories to manufacture Pozzolana and slag cements.