Finding a solution to chromium pollution in the Sukinda valley
The discovery of the Sukinda chromite field in Orissa was entirely accidental. "In the early 1950s, a native of Sukinda was working as a labourer in Tata's Jamshedpur steel plant. He picked up a boulder from his backyard, took it to the then superintendent of ores, mines and quarries in Tata Iron and Steel Company (tisco), who immediately recognised the material as chromite ore." Until this discovery, all tisco managed to mine were small inch-sized chromite chips. That one boulder of chromite led to the discovery of the largest chromite deposit in India, with bands of chromite ore that are several metres thick, and are mined just below the ground.
To add to the bounty, it was discovered that the even the over-burden material, which holds the thick chromite layers, were nickeliferous. Similarly, the Daitary hills skirting and enclosing the v-shaped Sukinda valley, have large quantities of iron ore. However, reports on the exposure of fuchsite quartzite (chromium bearing green quartzite), a rare and greatly valued ornamental building stone, are yet to receive much attention. With such a concentration of wealth underground, how will Sukinda valley hold its own?
Today, there is proof of the harmful effects of chromium pollution -- a matter that has been the subject of discussions for long. All natural chromium is found in a trivalent state (Cr-iii), and most of it is locked up in extremely refractory and inert chromite mineral. Chromium could, though, transform to the mobile hexavalent state (Cr-vi) if it is strongly heated with a corrosive oxidising reagent like soda ash to prepare chrome chemicals. The natural chromite deposit is not a health hazard. In fact, traces of the metal (biologically active chromium -- bac) received through foods have therapeutic value.
There are two types of chromite deposits in nature: one, known as layered type, subject to little alteration, and the alpine type, which is subject to alteration when in contact with water. The alpine type, when extensively oxidised could convert Cr-iii to Cr-vi. The Sukinda chromite deposit is believed to be of this type. A series of analyses, undertaken by the Indian Institute of Technology, Bombay (iit-b), of water and sediments from Damsala and Brahmani rivers show the generation of Cr-vi. Besides the chromite mines in the valley, the charge chrome factory at Jaipur road downstream, the Orichem industries, as well as the Talchir thermal plant, all contribute chromium (including Cr-vi) in dissolved, absorbed or particulate state to the lower section of Brahmani river.
Chromium toxicity in Sukinda has received much attetion, particularly with regard to health concerns (studies are yet to come up with conclusive evidence). However, the over-burden material generated and dumped around the mines, carrying toxic metals like nickel and cobalt, has received little attention. An iit-b study in Sukinda has shown extensive leaching and mobility of nickel and cobalt from solid particulate to pore water.
Creation of sediment traps by check dams across drainage channels to prevent particulate chromite movement. This gives the added advantage of watershed harvesting in the valley.
Goethite, the most common mineral in the laterite, is capable of cleaning chromium rich water through the percolation process. Similarly, manganese, which is abundant in the Sukinda valley topsoil, will help in 'dechromification'.
A separate investigation on dispersion of hexavalent chromium revealed that the chromite-laden effluent is extensively dechromified when the effluent passes through cattle sheds. The cattle sheds obviously provided the reducing environment for conversion of the mobile Cr-vi to Cr-iii, with consequent immobilisation of the element. Animal husbandry could, therefore, be developed as a supplementary vocation, and a parallel economy around mines.
The above measures need detailed local terrain analyses, information on the geomorphology, hydrology and soil characteristics for integrated land uses. A balanced approach would encourage the practice of agriculture and animal husbandry for integrated socio-economic development to counteract pollution in the valley.
K C Sahu is retired professor, Indian Institute of Technology, Bombay
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