A study by researchers at Dhanbad-based IIT(ISM) on the use of industrial waste as mine backfill has revealed economic and environmental benefits, including the prevention of sand overexploitation and solving the issue of waste disposal.

“The depletion of river sand due to overexploitation for various purposes, including its use 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 led our researchers to carry out a study on the feasibility of the use of industrial waste like mill tailings and fly ash as mine backfilling material,” said Rajni Singh, the spokesperson for IIT(ISM).

The study was conducted by Santosh Kumar Behera, a research scholar of IIT(ISM), as part of his PhD thesis under the guidance of the department head of mining engineering Devi Prasad Mishra and former chief scientist at Central Institute of Mining and Fuel Research (CIMFR) Dhanbad, C.N Ghosh.

The study revealed that the use of industrial wastes such as mill tailings substantially reduces the cost of mine backfilling and 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 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 spokesperson said.

“The use of industrial waste like fly ash 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 wasteland and, at the same time, prevents subsidence in the case of underground mines by stabilising the surface of the underground mines,” she added.

Mail tailings, which are byproducts of the beneficiation of underground metalliferous mines, are finer than sand and possess favourable 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 a filling material in mines, as it possesses pozzolanic properties and also requires less water and energy for its transportation.

“The PhD thesis mainly focused on the design and optimisation of paste backfill mix through lab experiments for backfilling in underground metalliferous mines,” said Behera, adding that the studies reveal that the utilisation of tailing, fly ash, slag, and other industrial waste as cemented paste backfill material reduces leaching risk compared with the use of uncemented surface disposal techniques.

“In India, there are four operating mines of Hindustan Zinc Ltd in Rajasthan adopting paste backfill technology, while two mines are under design implementation stage, including one of Hindustan Copper Ltd (Madhya Pradesh) and another of Uranium Corporation of India Ltd Jamshedpur,” Mishra said.