Offshore high-grade limemud resources of west coast of India: Economic potential and industrial applications

Abstract

Limestone is one of the essential raw materials in the cement, paint, steel, ceramic, glass, chemical, pharmaceutical, paper, and fertilizer industries. In India, only 8% of the limestone resources are placed under the reserve category, of which 97% is of cement grade. Thus, India depends on imports to bridge the demand-supply gap of steel, blast furnace, and chemical-grade limestone. Efforts of Geological Survey of India (GSI) to locate alternate sources for limestone led to the discovery of enormous quantities of carbonate minerals called limemud from the continental shelf margin of the west coast of India. GSI carried out systematic studies to explore the nature of the disposition, quality, quantity, and suitability of the offshore limemud for various industrial applications. A preliminary estimate of resources using high-resolution subbottom profiling and sediment core sample studies established the occurrence of more than 172 billion tonnes of high-grade (The content of CaCO₃ is greater than 80 wt%) limemud in 0.4–28.0 m thick stratified sediment layers spread over an area of 18 000 km². Chemical, physical, mineralogical, beneficiation, and agglomeration studies found the offshore limemud as a potential replacement for limestone in the cement, filler, blast furnace, steel melting shop, lime production, paint, and Grade-I steel industries. An assessment of mining and transportation costs indicates that the offshore limemud (USD 5–6/ton) is more cost-effective than that imported from other countries (USD16-18/ton). With several advantageous factors like low impurity, mode of occurrence in overburden-free stratified form, fine-grained slurry nature, and shallow water depth, sustainable mining of offshore limemud could be a future reality with controllable technological, economic, and environmental challenges.