EIACP (PC-RP) on Environmental Problems of Mining

STUDY OF THE POSSIBILITY OF UTILIZING FLY ASH FOR BACK FILLING AND RECLAMATION OF OPENCAST MINES: PLOT AND FIELD SCALE STUDY WITH CHANDRAPURA FLY ASH

S.K.Maiti, Gurdeep Singh, S.B. Srivastava

Centre of Mining Environment, Department of Environmental Science & Engineering
Indian School of Mines University , Dhanbad - 826 004

Published in:
Proceedings of Golden Jubilee Seminar on "Present Status of Mining and Future Prospects" April 6-8, 2007 at Hyderabad.

ABSTRACT

Fly ash (FA) is generated from combustion of coal in Thermal Power plants. The quantum of FA generated depends upon the quality of coal burnt and mainly the ash content of the coal. Currently, about 110 Million tonnes (MT) of FA is generated annually, and utilization has been increased up to 33 MT and 42 MT in the year 2003-04 and 2004-05 respectively. One of the major route of utilization of FA would be the backfilling and reclamation of abandoned opencast mine voids.

The FA experiment was conducted in an experimental plot and fly ash filled opencast mine pits. The experimental plot was filled with FA collected from Chardrapur Thermal Power Plant (CTPP) and allowed for natural plant succession. After one year, Cynodon dactylon was found growing profusely and covered the entire plot along with other species. A field study was undertaken in an opencast mine voids where approximately 2.5-3 MT of FA from CTPP was dumped and void was filled to the surface. The FA surface was covered with 40 - 60cm thick layer of topsoil and no plantation was carried out and left as it for the natural succession.

Metal accumulations pattern in the naturally growing vegetation on FA dyke and topsoil were studied. FA samples had neutral pH (5.45-6.52), low electrical conductivity (39.9-98.4 µS/cm), and low organic carbon, nitrogen and phosphorus. The relative abundance of bioavailable, acid extractable and total metals in FA was found in the order of: Fe> Mn> Zn> Ni > Co >Cu. The concentration of metals in plants served to indicate the metal contamination status and also the abilities of various plant species to take up and accumulate the metals from the FA. The total metal contents in roots and shoot portions for all the naturally occurring vegetation were studied. The variation of biological accumulation coefficient of metals for plants growing in the FA dyke was found as Fe>Zn> Mn >Pb> Ni >Cu > Co and Fe is the element most easily absorbed by plants. The study revealed Cynodon growing on topsoil accumulates more metals than FA and acts as “metal excluder species”.

In the earthen pot experiment 6 leguminous species belong to pulses type were selected and growth were studied at various combinations of FA and soil mixtures. The moisture retention capacities of different mixture revealed that after 7 days field moisture decreased to a level of 4.25% and irrigation is needed. The leaching study reveals that no significant leaching occurs would not to pose any environmental problems during its utilization and/or disposal. The study identified that for the successful mine fill operation following care must be taken; like proper contouring and drainage of the fill area, quality of topsoil which is used as cover material, proper spreading of topsoil and advance measures for the control of gully erosion.

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