Remediation and Selective Recovery of Metals from Acidic Mine

Sep 24, 2014 - Remediation and Selective Recovery of Metals from Acidic Mine Waters Using Novel Modular Bioreactors ... Citation data is made availabl...
1 downloads 12 Views 1MB Size
Subscriber access provided by Umea University Library

Article

Remediation and selective recovery of metals from acidic mine waters using novel modular bioreactors Sabrina Hedrich, and D. Barrie Johnson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es5030367 • Publication Date (Web): 24 Sep 2014 Downloaded from http://pubs.acs.org on October 3, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

Environmental Science & Technology

529x401mm (300 x 300 DPI)

ACS Paragon Plus Environment

Environmental Science & Technology

1

Remediation and selective recovery of metals from acidic

2

mine waters using novel modular bioreactors

Page 2 of 24

3

Sabrina Hedrich1,* and D. Barrie Johnson

4

5

6

School of Biological Sciences, College of Natural Sciences, Bangor University, Deiniol Road,

7

Bangor LL57 2UW, U.K.

8

1

9

2, 30655 Hanover, Germany

10

current address: Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg

*Corresponding author: e-mail: [email protected], Tel +49 0511-6423187

11

1 ACS Paragon Plus Environment

Page 3 of 24

Environmental Science & Technology

12

13

ABSTRACT

14

Mine waters are widely regarded as environmental pollutants, but are also potential sources

15

of valuable metals. Water draining the Maurliden mine (Sweden) is highly acidic (pH 2.3) and

16

rich in zinc (~460 mg L-1) and iron (~400 mg L-1), and contains smaller concentrations (0.3 -

17

49 mg L-1) of other transition metals and arsenic. We have developed novel techniques that

18

promote the concurrent amelioration of acidic waste waters and selective recovery of metals,

19

and have used these systems to treat synthetic Maurliden mine water in the laboratory. The

20

two major metals present were removed via controlled biomineralization: zinc as ZnS in a

21

sulfidogenic bioreactor, and iron as schwertmannite by microbial iron oxidation and

22

precipitation of ferric iron. A small proportion (~11%) of the schwertmannite produced was

23

used to remove arsenic as the initial step in the process, and other chalcophilic metals

24

(copper, cadmium and cobalt) were removed (as sulfides) in the stage 1 metal sulfide

25

precipitation

26

biomineralization units can be effective at processing complex mine waters and generating

27

metal products that may be recycled. The economic and environmental benefits of using an

28

integrated biological approach for treating metal-rich mine waters is discussed.

29

Keywords: Acid mine drainage; bio-mineralization; bioremediation; iron oxidation; sulfate

30

reduction; metal recovery, metal recycling

reactor.

Results

from

this

work

have

demonstrated

that

modular

31

32

33

34

35

2 ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 24

36

INTRODUCTION

37

Waters draining abandoned metal mines and mine wastes are often acidic (pH 99.9% of the

207

arsenic present could be successfully removed within 2 hours residence time, by adding 80

208

mg (dry weight) of the mineral per liter of synthetic mine water (Table S1, Figure S1). This

209

amount of schwertmannite was equivalent to ~11% of that produced from synthetic water in

210

module I.

211

Selective precipitation of transition metal sulfides. Hydrogen sulfide was produced in the

212

sulfidogenic bioreactor (stage 2 metal sulfide precipitation) in excess of that required to

213

precipitate zinc (as described below). This was transferred to the stage 1 metal sulfide

214

precipitation vessel in a N2-gas stream, at a rate of 4.5 µmoles h-1 (calculated from the mean

215

flow rate and the pH differential between that within the bioreactor and the liquor that flowed

216

into it, as described below). Over 99.9% of cadmium and copper in the synthetic mine water,

217

together with ~50% of nickel and ~3% of zinc, were precipitated (as sulfides) in the stage 1

218

metal sulfide precipitation vessel, but no removal of manganese or cobalt was detected

219

(Table S1, Figure 3).

9 ACS Paragon Plus Environment

Page 11 of 24

Environmental Science & Technology

220

The final stage in the mine water treatment protocol involved precipitating zinc (as ZnS)

221

within the acidophilic sulfidogenic bioreactor vessel (stage 2 metal sulfide precipitation;

222

Figure 1). By maintaining the pH within this reactor at 4.0, co-precipitation of aluminum (e.g.

223

as basaluminite) and manganese, both of which were still present in the part-processed

224

water at similar concentrations to those of Maurliden mine water, was avoided (data not

225

shown). Some members of the acidophilic sulfidogenic consortium had been found in

226

previous work to be sensitive to aluminum11, and therefore this metal was added

227

incrementally to the test liquor. As shown in Figure 4a, increasing the aluminum

228

concentration to 81 mg/L caused the performance of this module to decline initially (indicated

229

by slower inflow rates and less complete biomineralization of ZnS) but the consortium quickly

230

adapted to tolerate aluminum concentrations of up to 132 mg L-1 (the concentration in

231

Maurliden mine water).

232

Sixteen days after the biosulfidogenic module had been operating in continuous flow mode,

233

analysis of liquor inside the reactor showed that, although 93% (6.5 mM) of the glycerol in

234

the influent liquor had been oxidized, 5 mM acetic acid was present (Figure 4b). This was

235

due to the dominant aSRB in the sulfidogenic consortium at that time being

236

Desulfosporosinus M1 (Figure S2a) which is known to be an “incomplete oxidizer” of

237

glycerol, generating equimolar concentrations of acetic acid as a waste product17. Although

238

the concentration of acetic acid declined (to 3.4 mM) by day 20, the presence of such large

239

concentrations of acetic acid implied that the efficiency of H2S production was far less than

240

what was desirable. To alleviate this problem, the acidophilic heterotroph Acidocella

241

aromaticaT,

242

previously been shown to grow in syntrophic culture with Desulfosporosinus M1, converting

243

acetic acid into hydrogen and carbon dioxide, and that the hydrogen so-generated was used

244

as a secondary electron donor by the sulfidogen18. The introduction of Ac. aromatica PFBC

245

resulted in concentrations of acetic acid within the bioreactor to be lowered and maintained

246

at 98% of

249

that provided) with no loss in the efficiency of the module, in terms of both zinc precipitation

250

and production of net alkalinity.

251

T-RFLP analysis of the acidophilic sulfidogenic consortium within module II on day 16 (Figure

252

S2a) indicated that the dominant bacteria were both aSRB: Desulfosporosinus sp. M1 (70%

253

relative abundance) and strain CEB3 (24% relative abundance), a firmicute previously

254

detected in the acidophilic sulfate-reducing consortia used in these experiments11. The other

255

bacterium detected in module II with minor abundance (6%) was the facultatively aerobic

256

chemolithotroph Acidithiobacillus ferrooxidans (~5% relative abundance). A T-RFLP profile

257

obtained at day 63 (Figure S2b), after Ac. aromatic PFBC had been added to the consortium,

258

showed that, although all three of the previously detected bacteria were still present, their

259

relative proportions had changed (38% Desulfosporosinus M1, 30% Ac. aromatica PFBC,

260

24.5% strain CEB3 and 1.5% At. ferrooxidans). One minor T-RF, of 130 nt (6%) length was

261

not identified.

262

263

DISCUSSION

264

Mine water generated as a waste product at the Maurliden mine contains relatively high

265

concentrations of two metals (iron and zinc), and smaller concentrations of several other

266

cationic metals, as well as anionic arsenic. The objectives in these trials were to recover zinc

267

and iron as potentially saleable products and to remove arsenic and most of the other metals

268

present in the mine water as a remediation strategy. The integrated bioreactor modules were

269

highly effective in meeting these objectives. Zinc was removed from the synthetic mine water

270

as ZnS, from which the metal could be recovered, as is the case at the Budel zinc refinery in

271

The Netherlands19.The much lower price of iron on the commodities market would suggest

272

that making a bio-mineral (schwertmannite) that has potential value both as a pigment and

273

as an adsorbent of (anionic) pollutants20,

21

is a more commercially-viable alternative for 11

ACS Paragon Plus Environment

Page 13 of 24

Environmental Science & Technology

274

recovering and recycling this metal. This was illustrated to some extent in the present study,

275

where ~11% of the schwertmannite produced was used to remove arsenic upstream of the

276

bioreactor modules, thereby concentrating this toxic metalloid rather than allowing it to co-

277

precipitate as a diffuse toxin in a sludge or spent compost. Therefore schwertmannite

278

harvested from module 1 can easily be applied in immobilized beds to adsorb arsenic from

279

mine waters in a similar setup as described by Janneck et al.21.

280

The water generated from the bio-processing system described was moderately acidic (pH

281

4.0) and contained only aluminum and manganese as residual (non basic) metals. Removing

282

these two metals was not an objective of the current research program, but further controlled

283

pH amelioration of the mine water (e.g. by addition of sodium hydroxide) would allow both

284

metals to be selectively precipitated, e.g. as basaluminite (Al4(SO4)(OH)10*4-5H2O) and

285

rhodochrosite (MnCO3). Manganese can also be removed using microbially-catalyzed

286

oxidation of Mn(II) to Mn(IV) and mineralization of MnO2 22.

287

The rationale of the module configuration used in the present trials was dictated by the mine

288

water chemistry. About 50% of the soluble iron in Maurliden mine water is present as ferric

289

iron. If the sulfidogenic bioreactor was used as the first treatment module, much of the

290

hydrogen sulfide generated would be used to reduce this to ferrous iron, generating

291

elemental sulfur as a co-product (2Fe3+ + H2S → 2Fe2+ + S0 + 2H+). This would both be

292

wasteful of the electron donor (glycerol) used to generate H2S, and also induce unnecessary

293

iron cycling. This necessitates the oxidation of the ferrous iron in the mine water which, at the

294

pH of the mine water, needs to be microbially-mediated.

295

The iron oxidation/precipitation module was highly effectively in generating relatively pure

296

schwertmannite, with most (>99.9%) of the iron present in the synthetic mine water

297

precipitated as schwertmannite. Residual ferrous iron could, if required, be removed using a

298

“polishing” packed bed bioreactor, as described by Hedrich and Johnson9. Soluble iron would

299

not, in any case, be precipitated in the sulfidogenic bioreactor as the pH is too low for this11.

12 ACS Paragon Plus Environment

Environmental Science & Technology

Page 14 of 24

300

Even so in this study the iron-oxidation module was operated under sterile conditions, this

301

would not be possible in large scale applications. Studies in our laboratory using the same

302

setup but operated under non-sterile conditions, however, shown that ferrous iron was

303

oxidized with the same efficiency and the microbial streamer community was still dominated

304

by “Fv. myxofaciens” but accompanied by another iron-oxidizer Acidithiobacillus ferrooxidans

305

and the heterotroph Acidiphilium sp.23.

306

The sodium hydroxide used to precipitate the schwertmannite in module I has not only the

307

advantage of lower reagents costs, compared to lime (calcium oxide) frequently used in

308

neutralization of acidic mine waters, but also avoids formation of gypsum in the high sulfate

309

mine waters and is more compatible for the microorganisms in the sulfidogenic system

310

(module II).

311

The low pH sulfidogenic bioreactor is a novel and integral component of the

312

bioremediation/metal recovery system described, as it serves both to capture transition

313

metals (as sulfides) and to increase mine water pH. It has an empirical operational design,

314

whereby acidic mine water is pumped into the bioreactor at a rate required to maintain pH

315

homeostasis, achieved using a pH electrode and meter coupled to a pump11. Most of the

316

hydrogen sulfide generated was used to precipitate ZnS in the bioreactor vessel itself, in a

317

theoretically pH-neutral reaction (the alkalinity of sulfate reduction being counterbalanced by

318

protons generated by the reaction between Zn2+ and H2S, equation 1b). Production of small

319

amounts of H2S in excess of that required to precipitate Zn2+ (“free H2S”) allowed the pH of

320

the reactor to be poised above that of the mine water (a pre-requisite of the modus operandi

321

of the module). This free H2S was used to remove copper and cadmium (also as sulfides)

322

upstream of the main sulfidogenic reactor in another metal sulfide precipitation stage,

323

thereby avoiding co-precipitation within and contamination of, the main ZnS product. The

324

very small solubility products of cadmium and copper sulfides (log Ksp values of -28.9 and -

325

35.9, respectively10) mean that these precipitate at lower pH than many other metals,

326

including cobalt, nickel and zinc. However, the much larger concentration of zinc than other 13 ACS Paragon Plus Environment

Page 15 of 24

Environmental Science & Technology

327

chalcophilic metals resulted in some formation of small concentrations of ZnS in the pH 3.2

328

stage 1 metal sulfide precipitation vessel, even though its log Ksp value (-24.5) is greater than

329

those of cadmium and copper. The amount of free H2S generated by the sulfidogenic reactor

330

was controlled by the flow rate and the pH differential between the influent liquor and that

331

within the reactor. For the trial period, the pH differential (3.2 vs. 4.0) was equivalent to 430

332

µM H+, and the mean flow rate was 47.5 ml h-1. Since net proton consumption was due to

333

H2S production (7SO42- + 4C3H8O3 + 14H+ → 7H2S + 12CO2 + 16H2O) this was equivalent to

334

4.53 µmoles of free H2S being generated h-1. Over two days, 76 µmoles of divalent transition

335

metals (2 µmoles Cd, 25 µmoles Cu and 49 µmoles Zn) were precipitated in the stage 1

336

metal sulfide precipitation bottle, whereas ~217 µmoles of H2S were calculated to have been

337

generated in the same time period.

338

The flow rates of mine water through the aerobic and anaerobic modules, which were of

339

similar working volumes, were very different (equivalent to a HRT of 1.96 H in the iron

340

oxidation/precipitation reactor and 41.7 H in the sulfidogenic bioreactor) since rates of iron

341

oxidation were much greater than those of sulfate reduction. This would necessitate the

342

sulfidogenic bioreactor being much larger than the schwertmannite-generating module in a

343

full-scale system. Based on the chemical data listed in Table 1, treating 1 m3 of Maurliden

344

mine water h-1 would require a 2 m3 iron oxidation bioreactor (and a similar sized

345

schwertmannite mineralization reactor) coupled to a 42 m3 sulfidogenic reactor. The reagent

346

costs (m-3 mine water) would be ~ $0.60 for sodium hydroxide and ~ $0.50 for glycerol. The

347

value of the zinc in the ZnS product is ~ $0.80 (on the basis that 0.46 kg can be recovered

348

from each m3 of mine water). Schwertmannite (~0.69 kg produced m -3 mine water) could be

349

sold, e.g. as a pigment, though the commercial value of this product is unpredictable. The

350

production of materials that have commercial value can therefore offset, at least in part, the

351

cost of the treatment process. Remediation of mine waters, such as that at the Maurliden

352

mine, using conventional chemical treatment, and disposal of the mixed metal sludges

353

produced has a substantial financial cost and inherent environmental risk (long-term

354

remobilization of metals and metalloids). Using an integrated biological process like that 14 ACS Paragon Plus Environment

Environmental Science & Technology

Page 16 of 24

355

described can, by generating separate mineral products, eliminate most if not all of the costs

356

and risks involved in disposing of mine water waste products.

357

Although described here for application to a particular mine water, the modular systems

358

described can be modified and configured to optimize remediation and metal recovery in

359

mine waters with very different chemistries, and represents an alternative, more

360

environmentally-benign and sustainable approach to mine water treatment for the 21st

361

century.

362

363

ACKNOWLEDGEMENTS

364

This work was carried out in the frame of ProMine (European project contract NMP-2008-

365

LARGE-2:# 228559). SH and DBJ acknowledge the financial support given to this project by

366

the European Commission under the Seventh Framework Program for Research and

367

Development, and to help give by colleagues at Boliden AB. We would like to thank Nils-

368

Johan Bolin (Boliden) for his advice and helpful comments.

369

370

SUPPORTING INFORMATION

371

The Supporting information contains two additional figures presenting the results of arsenic

372

adsorption onto schwertmannite and T-RFLP analysis of the sulfidogenic bioreactor

373

consortium.

374

375

REFERENCES

376

(1) Nordstrom, D.K. Advances in the hydrogeochemistry and microbiology of acid mine

377

waters. Int. Geol. Rev. 2002, 42, 499 515.

378

(2) Langdahl, B. R.; Ingvorsen, K. Temperature characteristics of bacterial iron solubilisation 15 ACS Paragon Plus Environment

Page 17 of 24

Environmental Science & Technology

14

379

and

C assimilation in naturally exposed sulfide ore material at Citronen Fjord, Greenland

380

(83°N). FEMS Microbiol. Ecol. 1997, 23, 275 283.

381

(3) Johnson, D. B. Chemical and microbiological characteristics of mineral spoils and

382

drainage waters at abandoned coal and metal mines. Water Air Soil Poll: Focus 2003, 3, 47

383

66.

384

(4) Schippers, A.; Breuker, A.; Blazejak, A.; Bosecker, K.; Kock, D.; Wright, T.L. The

385

biogeochemistry and microbiology of sulfidic mine waste and bioleaching dumps and heaps,

386

and novel Fe(II)-oxidizing bacteria. Hydrometallurgy 2010, 104, 342 350.

387 388

(5) Johnson, D.B.; Hallberg, K.B. Acid mine drainage: remediation options. Sci.Total Environ.

389

2005, 338, 3 14.

390

(6) Tabak, H.H.; Govind, R. Advances in biotreatment of acid mine drainage and biorecovery

391

of metals: 2. membrane bioreactor system for sulfate reduction. Biodegradation 2003, 14,

392

437 452.

393

(7) Tabak, H.H.; Scharp, R.; Burckle, J.; Kawahara, F.K.; Govind, R. Advances in

394

biotreatment of acid mine drainage and biorecovery of metals: 1. metal precipitation for

395

recovery and recycle. Biodegradation 2003, 14, 423 436.

396

(8) Ňancucheo, I.; Hedrich, S.; Johnson, D.B. New (micro-)biological strategies that enable

397

the selective recovery and recycling of metals from acid mine drainage and mine process

398

waters. Min. Mag. 2012, 76, 2683 2692.

399

(9) Hedrich, S.; Johnson, D. B. A modular continuous flow reactor system for the selective

400

bio-oxidation of iron and precipitation of schwertmannite from mine-impacted waters.

401

Bioresource Technol. 2012, 106, 44 49.

402

(10) Stumm, W., Morgan, J. J., 1996. Aquatic chemistry: chemical equilibria and rates in

16 ACS Paragon Plus Environment

Environmental Science & Technology

Page 18 of 24

403

natural waters; John Wiley & Sons: New York.

404

(11) Ñancucheo, I.; Johnson, D. B., Selective removal of transition metals from acidic mine

405

waters by novel consortia of acidophilic sulfidogenic bacteria. Microbial. Biotechnol. 2012, 5,

406

34 44.

407

(12) Hedrich, S.; Schlömann, M.; Johnson, D.B. The iron-oxidizing Proteobacteria.

408

Microbiology 2011, 157, 1551 1564.

409

(13) Lovley, D.R.; Phillips, E.J.P. Rapid assay for microbially reducible ferric iron in aquatic

410

sediments. Appl. Environ. Microbiol.1987, 53, 1536 1540.

411

(14) Lane, D. J. 16S/23S rRNA sequencing. In Nucleic acid techniques in bacterial

412

systematic. E. Stackebrandt, M.G., Eds., John Wiley and Sons, New York 1991, pp 115.

413

(15) Marchesi, J. R.; Sato, T., Weightman, A. J.; Martin, T. A.; Fry, J. C.; Hiom, S. J.;

414

Dymock, D.; Wade, W. G. Design and evaluation of useful bacterium-specific PCR primers

415

that amplify genes coding for bacterial 16S rRNA. Appl. Environ. Microbiol. 1998, 64, 795

416

799.

417

(16) Okibe, N.; Gericke, M.; Hallberg, K. B.; Johnson, D. B. Enumeration and

418

characterization of acidophilic microorganisms isolated from a pilot plant stirred tank

419

bioleaching operation. Appl. Environ. Microbiol. 2003, 69, 1936 1943.

420

(17) Jones, R. M.; Hedrich, S.; Johnson, D. B. Acidocella aromatica sp. nov.: an acidophilic

421

heterotrophic alphaproteobacterium with unusual phenotypic traits. Extremophiles 2013, 17,

422

841-850.

423

(18) Kimura, S.; Hallberg, K. B., Johnson, D. B. Sulfidogenesis in low pH (3.8 – 4.2) media by

424

a mixed population of acidophilic bacteria. Biodegradation 2006, 17, 57 65.

425

(19) Boonstra, J.; et al. Biological treatment of acid mine drainage. In Biohydrometallurgy and

426

the Environment Toward the Mining of the 21st Century; Amils, R., Ballester, A., Eds., 17 ACS Paragon Plus Environment

Page 19 of 24

Environmental Science & Technology

427

Process Metallurgy 9B. Elsevier: Amsterdam 1999, pp 569.

428

(20) Carlson, L.; Bigham, J.M.; Schwertmann, U.; Kyek, A.; Wagner, F. Scavenging of As

429

from acid mine drainage by schwertmannite and ferrihydrite: a comparison with synthetic

430

analogues. Environ. Sci. Technol. 2002, 36, 1712 1719.

431 432

(21) Janneck, E.; et al. Microbial synthesis of schwertmannite from lignite mine water and its

433

utilization for removal of arsenic from mine waters and for production of iron pigments. In

434

Proceedings IMWA 2010 “Mine water and innovative thinking”; Wolkersdorfer, C; Freund, A.,

435

Eds., CBU Press, Sydney, Canada 2010, pp 131.

436

(22) Sasaki, K.; Konno, H; Endo, M.; Takano, K. Removal of Mn(II) ions from aqueous

437

neutral media by manganese-oxidizing fungus in the presence of carbon fiber. Biotechnol.

438

Bioeng. 2004, 85, 489 496.

439 440

(23) Kay, C.M.; Hedrich, S.; Johnson, D.B. Selective metal removal from scandinavian mine

441

waters using novel biomineralization technologies. Adv. Mat. Res. 2013, 825, 479-482.

442

18 ACS Paragon Plus Environment

Environmental Science & Technology

Page 20 of 24

443

444

Table 1. Concentration of the major components of Maurliden mine water (data obtained

445

from Boliden AB, Sweden). Analyte

Concentration

Analyte

[mg/L]

Concentration [mg/L]

Zn

464

Cd

1.0

Fe (II)

200

Co

0.4

Fe (III)

203

Ni

0.3

Al

132

Ca

271

Mn

49

Mg

123

Cu

7.7

Na

13.8

As

1.3

K

4.0

446

19 ACS Paragon Plus Environment

Page 21 of 24

Environmental Science & Technology

447 448

Figure 1. Schematic representation of the integrated system used to remediate synthetic

449

Maurliden mine water and to recover iron and zinc as mineral products.

450

20 ACS Paragon Plus Environment

Environmental Science & Technology

451 452 453 454 455 456

Page 22 of 24

Figure 2. Changes in (a) pH (•) and concentrations of ferrous (□) and ferric iron (■), and (b) of aluminum (◊), copper (∆), manganese (●) and zinc (▲) during passage of synthetic Maurliden mine water through the iron oxidation/precipitation module I. Effluent (i) is water draining the iron oxidation bioreactor and effluent (ii) is water draining the schwertmannite precipitation vessel. The hydraulic residence time in both vessels was 1.96 H.

457 458 459 460

21 ACS Paragon Plus Environment

Page 23 of 24

Environmental Science & Technology

461 462 463 Mn

464 Cu

465 Cd

466

Co

467

Ni

468 469 470 471 472 473 474 475

Figure 3. Changes in concentrations of transition metals in synthetic Maurliden mine water in the stage 1 metal sulfide precipitation vessel receiving H2S generated in module II. Zinc is not shown, but declined from 464 to 450 mg L-1 during the 2 day experiment.

22 ACS Paragon Plus Environment

Environmental Science & Technology

Page 24 of 24

476 477 478

(a)

479 480 481 482 483 484 485 486 487 (b)

488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503

Figure 4. Changes in (a) flow rates (□) and concentrations of soluble zinc (●), and (b) concentrations of glycerol (●) and acetic acid (□), in the sulfidogenic bioreactor (module II). The downward-pointing arrows indicate addition of aluminum: (i) 1 mM, (ii) 2 mM, (III) 3 mM), (iv) 4 mM, (v) 5 mM. The upward-pointing arrow indicates the addition of an active culture of Acidocella aromaticaT to the sulfidogenic bioreactor.

504 505

23 ACS Paragon Plus Environment