The steady depletion of river sand due to overexploitation for various purposes, including its usage as construction material and also as the main source of mine backfill material, and the resultant increase in the cost of mine backfilling due to the increase in sand mining and transportation costs have propelled IIT (ISM) researchers to carry out an extensive study on the feasibility of the usage of industrial waste like mill tailings and fly ash as mine backfilling material.

The study conducted by Santosh Kumar Behera, a research scholar of IIT (ISM), as part of his PhD thesis, under the guidance of Prof Devi Prasad Mishra, Head of Department of Mining Engineering of the institute, as Supervisor, and also under CN Ghosh, Former Chief Scientist of Central Institute of Mining and Fuel Research (CIMFR) as Co Supervisor, revealed that the usage of industrial wastes like mill tailings substantially reduces the cost of mine backfilling and at the same time also prevents the overexploitation of river sand.

The study titled, “Geomechanical and Microstructural Investigations of Lead Zinc Mill Tailings-Based Paste Backfill for Underground Metalliferous Mines” underscores the use of industrial wastes as mine backfill material and the resultant conservation of river sand in order to help prevent the ill effects of overexploitation of sand, like alteration of the river bed, change of course of the river, and erosion of the river bank causing flooding.

The use of industrial waste like flyash and Mail Tailings can also help to address the problem of their disposal. Backfilling is an important component of the overall mining cycle as it helps in the reclamation of mine waste land and, at the same time, helps to prevent subsidence in the case of underground mines by stabilizing the surface of the underground mines. Mail tailings, which are byproducts of the beneficiation of underground metalliferous mines, are finer as compared to sand and possess favorable properties for use as paste backfill material.

The fine-grained fly ash generated by thermal power plants can also be a good substitute for sand as filling material in mines, as it possesses pozzolanic properties and also requires less water and energy for its transportation.

In the recently completed PhD thesis, fly ash, fuming furnace slag (FFS), lead zinc mill tailing, and crushed fuming slags have been used as paste-back fill material for underground metalliferous mines.

“The PhD thesis mainly focused on the design and optimization of paste backfill mix through lab experiments for backfilling in underground metalliferous mines,” said Behera, adding that studies reveal that the utilization of tailing, flyash, slag, and other industrial wastes as cemented paste backfill material reduces the leaching risk compared to the usage of uncemented surface disposal techniques.

“In India, presently, there are four operating mines of Hindustan Zinc Limited in Rajasthan State adopting paste backfill technology, while two mines are under design implementation stage, including one of  Hindustan Zinc Limited and another of Uranium Corporation of India Limited (UCIL)," revealed Prof. Mishra.

"Globally, more than 100 underground metalliferous mines use paste backfill technology, so there is enough scope for applying paste backfill technology on a large scale in India,” said Prof. Mishra, adding that though there are several cases of use of paste backfill in underground metal mines, the application of paste backfilling in underground coal mines is negligible.

“Though the present share of underground coal production is a meager 5% in India, future trends indicate a gradual rise in the share and a resultant increase in paste backfill material in the future,” said Mishra, adding that conventional backfill technology can’t match the higher rate of production from underground 

mines.