Wa­ter in Min­ing

The Australian Mining Review - - CONTENTS -

WA­TER is es­sen­tial to min­eral pro­cess­ing, and is used at var­i­ous steps in the process to re­cover valu­able met­als from ore.

The wa­ter use is quite high – for ex­am­ple, around 1600 litres of wa­ter is used to ob­tain about 19kg of cop­per – about the same as is needed for man­u­fac­tur­ing a medium-sized fam­ily car.

How­ever the min­ing sec­tor is a rel­a­tively small wa­ter user, ac­count­ing for less than 3.7 per cent of na­tional wa­ter con­sump­tion in 2014-15.

By com­par­i­son, agri­cul­ture (in­clud­ing forestry and fish­ing) con­sumed 60 per cent and house­holds con­sumed a fur­ther 12 per cent.

Ac­cord­ing to the Min­er­als Coun­cil of Aus­tralia, the min­ing sec­tor is one of the high­est value wa­ter users in Aus­tralia.

In 2016-17, the gross value add per gi­gal­itre (GL) of wa­ter used by min­ing ranged be­tween $111m/GL and $127m/GL, com­pared to $4m/ GL for agri­cul­ture.

Valu­ing Wa­ter

Wa­ter avail­abil­ity and se­cu­rity of sup­ply is crit­i­cal for the min­er­als in­dus­try.

Min­ers face a wide va­ri­ety of wa­ter man­age­ment chal­lenges, in­clud­ing lim­ited wa­ter sup­ply, use and treat­ment of poor qual­ity wa­ter, mine de­wa­ter­ing and the man­age­ment of ex­cess wa­ter.

Op­er­a­tions are re­quired to in­stall, op­er­ate and main­tain the in­fra­struc­ture when nec­es­sary for their wa­ter sup­ply, and in some cir­cum­stances the wa­ter in­fra­struc­ture pro­vided and main­tained by in­dus­try can be shared with other stake­hold­ers, in­clud­ing neigh­bour­ing com­mu­ni­ties, farm­ers and pas­toral­ists.

Many min­ing op­er­a­tions are based in re­mote lo­ca­tions, where wa­ter may not be read­ily avail­able.

This can rep­re­sent a sig­nif­i­cant po­ten­tial con­straint on fur­ther in­vest­ment and ex­pan­sion.

Even en­vi­ron­ments where it is ac­ces­si­ble, pro­cesses for mak­ing the wa­ter suit­able for use in the refin­ing process (such as de­salin­i­sa­tion) can add sig­nif­i­cant costs through in­creased en­ergy use.

As ore grades de­cline, the amount of wa­ter used in­creases and more in­ten­sive pro­cess­ing is re­quired.

Stud­ies con­ducted by the CSIRO sug­gest min­ing lower grade ore is be­com­ing more preva­lent in Aus­tralia, and the re­search group has re­sponded by look­ing at ways to es­ti­mate wa­ter foot­prints for ma­jor min­eral com­modi­ties such as nickel, cop­per and gold.

“By in­ves­ti­gat­ing meth­ods of valu­ing wa­ter in min­ing, min­eral pro­cess­ing and metal pro­duc­tion, and com­par­ing these with other in­dus­trial pro­cesses and wa­ter users, we will be able to bet­ter man­age wa­ter and re­duce the risk of wa­ter scarcity,” the CSIRO stated.

The method is a tech­nique called life cy­cle as­sess­ment.

“Us­ing our method, in­dus­try can mea­sure and an­a­lyse its wa­ter foot­print from the point where ore is ex­tracted through the pro­duc­tion process, and on to its end use and dis­posal.

“Op­er­a­tors can iden­tify and cal­cu­late the di­rect wa­ter use of var­i­ous pro­cesses such as milling and flota­tion as well as in­di­rect wa­ter use.

“Wa­ter use ‘hotspots’ can be de­tected and op­por­tu­ni­ties for wa­ter sav­ings – and the as­so­ci­ated cost ben­e­fits – high­lighted.

“It is lead­ing to more sus­tain­able min­er­als pro­cess­ing op­er­a­tions.”

Col­lab­o­ra­tions be­tween in­dus­try and sci­en­tists, such as the Pil­bara Wa­ter Re­source As­sess­ment project, have ex­am­ined wa­ter ecosys­tems and how they change dur­ing wet and dry pe­ri­ods.

The $3.5 mil­lion part­ner­ship be­tween the CSIRO, BHP Bil­li­ton and the WA Gov­ern­ment, was aimed to aid wa­ter man­agers and lo­cal

Wa­ter scarcity can rep­re­sent ad­di­tional costs for busi­nesses, which makes on­go­ing stud­ies on how we ac­cess, use and re-use it in in­dus­tries – such as min­ing – in­valu­able.

in­dus­try plan for fu­ture wa­ter use in an area rich in re­sources and en­vi­ron­men­tal as­sets.

The study re­vealed some of the mech­a­nisms re­spon­si­ble for fill­ing the Pil­bara’s ground­wa­ter stores.

It found that be­tween 8mm and 30mm of rain­fall is re­quired be­fore runoff starts in most catch­ments, which leaks through streambeds to pro­vide the main source of aquifer re­plen­ish­ment.

Wa­ter from these shal­low al­lu­vial aquifers then recharges deeper dolomite aquifers, which can store large quan­ti­ties of wa­ter in in­land ar­eas.

“Know­ing how the wa­ter sys­tems op­er­ate right across the re­gion, such as how ground­wa­ter is af­fected by rain­fall and storm events, helps with the plan­ning and man­age­ment of lo­cal wa­ter use,” CSIRO project leader Dr Don McFar­lane said.

PROJECT SNAPSHOT Nolans: Ground­wa­ter As­sess­ment

In early Jan­uary, the NT En­vi­ron­men­tal Pro­tec­tion Agency (EPA) ap­proved Ara­fura Re­sources’ $900m Nolans rare earths project, 135km north­west of Alice Springs.

As part of its study, the EPA iden­ti­fied a risk to the sta­bil­ity of ground­wa­ter lev­els, cit­ing that the project would use 2.7 gi­gal­itres of ground­wa­ter each year over a lengthy mine life of be­tween 35 and 55 years – but found that it could be man­aged.

In Ara­fura’s En­vi­ron­men­tal Im­pact State­ment (EIS) sub­mis­sion to the EPA, the ground­wa­ter model pre­sented in­di­cated that the open pit would be­come a per­ma­nent ground­wa­ter sink with es­ti­mated in­flows of eight litres a se­cond.

“This would re­sult in a con­tin­u­ous draw­down of ground­wa­ter sur­round­ing the pit,” the EPA said.

“At the end of mine life the open pit would con­tain a pit lake that would reach equilib­rium where evap­o­ra­tion matches in­flows, at a level 80m be­low the orig­i­nal aquifer depth.”

The EPA pro­jected that the pit lake that would be left be­hind af­ter the end of Nolans’ mine life would not harm the sur­round­ing ge­ol­ogy.

“The ground­wa­ter sink from the pit is not pre­dicted to have any sig­nif­i­cant im­pact on the high qual­ity aquifers of the Ti Tree Basin and South­ern Basins af­ter clo­sure of the project be­cause the rock base­ment con­nect­ing these aquifers has very low trans­mis­siv­ity.”

How­ever, it noted there would be un­cer­tain­ties sur­round­ing the be­hav­iour of the pit lake post-clo­sure.

“The NT EPA con­sid­ers fur­ther stud­ies are re­quired on the fi­nal void wa­ter qual­ity in­clud­ing the sur­round­ing ground­wa­ter level and ex­pected qual­ity of wa­ter held in the void prior to fi­nal ac­cep­tance of the mine clo­sure plan.”

It rec­om­mended that aquifer lev­els and wa­ter us­age be mon­i­tored in real-time with data made avail­able to the pub­lic on a reg­u­lar ba­sis.

The EPA also rec­om­mended that Ara­fura con­duct risk-based as­sess­ments of the im­pacts of on sty­go­fauna in the re­main­ing ground­wa­ter.

Ara­fura said it was happy with the EPA’s rec­om­men­da­tions and looked for­ward to fur­ther mine plan­ning, with a view to start con­struc­tion in 2019.

“Our sus­tain­abil­ity team has worked dili­gently along­side our en­vi­ron­men­tal con­sul­tants GHD to pro­duce com­pre­hen­sive, qual­ity doc­u­men­ta­tion to sup­port the pas­sage of the Nolans project through the North­ern Ter­ri­tory en­vi­ron­men­tal ap­provals process,” Ara­fura manag­ing di­rec­tor Gavin Lock­yer said.

“This should go some way to se­cur­ing fi­nal gov­ern­ment ap­proval for the project, en­abling con­struc­tion to move for­ward, sub­ject to fi­nanc­ing and FID.”

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.