En­vi­ron­men­tal Im­pact of Acid Mine Drainage and over­view of the Treat­ment Tech­niques

Dr A Gan­gagni Rao, Chief Sci­en­tist, CSIR – IICT; Dr San­deep Panda, SERB Na­tional Post Doc Fel­low, CSIR – IICT; Sameena Begum, Royal Mel­bourne In­sti­tute of Tech­nol­ogy, Aus­tralia

Chemical Industry Digest - - What’s In? -

This ar­ti­cle fo­cuses on the ori­gin, causes, en­vi­ron­men­tal im­pact of acidic waste­water gen­er­ated from the min­ing in­dus­try, also known as the Acid Mine Drainage. The ar­ti­cle also gives an over­view of the treat­ment tech­niques of such waste­water.

Ab­stract

Acidic wastew­a­ters gen­er­ated from the min­ing in­dus­tries are re­ferred to as Acid Mine Drainage (AMD) and are known to be as­so­ci­ated with se­ri­ous en­vi­ron­men­tal prob­lems. The dis­so­lu­tion of heavy met­als and toxic sub­stances into the en­vi­ron­ment, as a re­sult of AMD, cause se­ri­ous con­cerns to the wa­ter­ways and bio­di­ver­sity. Over the years, sev­eral treat­ment tech­niques have sur­faced for AMD man­age­ment and safe treat­ment. The present ar­ti­cle fo­cuses on the ori­gin, causes, en­vi­ron­men­tal im­pact of AMD along with an over­view of the avail­able treat­ment tech­niques.

Min­ing ac­tiv­i­ties have been prac­tised for cen­turies for the com­mer­cial ex­ploita­tion of min­eral re­sources to meet the grow­ing de­mand for met­als. Ex­ten­sive min­ing ac­tiv­i­ties for ex­trac­tion of met­als, like - cop­per, gold, nickel etc., from their sul­phides, re­sults in the gen­er­a­tion of wastes such as “waste rocks” and “mine tail­ings” at the mine site, which is dumped( 1). The dumped wastes at the mine site gen­er­ally come in con­tact with air and wa­ter (ground or rain wa­ter) that re­sults in its weath­er­ing. This gen­er­ates acids and toxic sub­stances. The weath­er­ing of the metal sul­phides can

be chem­i­cal, hy­dro­log­i­cal or mi­cro­bi­o­log­i­cal( 2). Wa­ters gen­er­ated ei­ther from the waste dumps or aban­doned mines are highly acidic and have el­e­vated lev­els of heavy met­als due to the weath­er­ing of the sul­phide min­er­als. Acid Mine Drainage (AMD) is thus an acidic waste­water, rich in met­als and other toxic sub­stances, gen­er­ated from a min­ing site (ex­am­ple - coal or any metal sul­phide mine). The dis­solved met­als and acids seep and mix into nearby wa­ter bod­ies caus­ing con­cerns to the wa­ter­ways and bio­di­ver­sity.

The min­ing sec­tor in In­dia plays an im­por­tant role in the coun­try’s econ­omy. In­dia stands to be the third largest pro­ducer of coal. For the year 2018, pro­duc­tion of coal in the coun­try has been es­ti­mated to be 676.51 mil­lion tonnes. In terms of pro­duc­tion of iron ore, In­dia stands to be in the 4th po­si­tion glob­ally with a pro­duc­tion re­ported to 210 mil­lion tonnes FY 2018.( This in­di­cates that iron ores

6) or iron as part of other ores con­sti­tute to be a ma­jor el­e­ment of the min­eral de­posits. Gen­er­ally, iron is seen as iron pyrites (FeS ) when it oc­curs in sul­phide form

2

(de­tails dis­cussed be­low w.r.t. AMD for­ma­tion). AMD is a com­mon prob­lem in coal or other sul­phide-rich mines and re­ports on its treat­ment in In­dia are scarce. Re­cently, Vyawahre and Rai (2016) have at­tempted two types of pas­sive treat­ment meth­ods for treat­ment of AMD from Dur­ga­pur mines, Ma­ha­rash­tra. It is be­lieved that, in the com­ing years, treat­ment of AMD will be an at­trac­tive area of re­search in In­dia.

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