Int. J. Miner. Process. 93 (2009) 103–109

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Int. J. Miner. Process.

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Treatment of Acid Mine Drainage (AMD) in South BrazilComparative active processes and water reuse

Aline Nogueira da Silveira, Renato Silva, Jorge Rubio ⁎Laboratório de Tecnologia Mineral e Ambiental (LTM), Departamento de Engenharia de Minas, PPGEM, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500/75,91501-970, Porto Alegre, RS, Brazil

⁎ Corresponding author. Tel.: +55 51 33089479; fax:E-mail addresses: alinenogueira_2000@yahoo.com.b

renato.dantas@ufrgs.br (R. Silva), jrubio@ufrgs.br (J. RubURL: http://www.ufrgs.br/ltm (J. Rubio).

0301-7516/$ – see front matter © 2009 Elsevier B.V. Aldoi:10.1016/j.minpro.2009.06.005

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 October 2008Received in revised form 8 May 2009Accepted 23 June 2009Available online 4 July 2009

Keywords:AMDLamella settlingFlotationWater reuse

This work describes AMD techniques of neutralization, with lime, flocculation of the precipitates andcomparative flocs/liquid separation by flotation with microbubbles or by lamellar settling (LS). The AMDtreated water was characterized by its quality for recycling in terms of inorganic or organic elements,suspended or dissolved solids, among others. Two types of flocs were formed, “aerated” or not, in a specialflocculation reactor, patented by this research group (RGF®). Aerated flocs formed (within seconds) enteredinto contact with microbubbles under high shearing and raised-up at ratesN120mh−1 allowing a rapidsolid–liquid separation by flotation (HR-high rate), at about 13–15m3m−2h−1 loading capacity. Conversely,the non-aerated flocs settled at about 5–6 m h−1 in a lamella settler. Both AMD treatment techniquesshowed similar efficiencies (removal of ionsN90%) but the separation by lamella settling presentedadvantages, namely less reagents (no flotation collector required), lower power requirements and easier tooperate. The operating costs (approximate values) of the AMD treatment by LS at pH 9 reaches about 0.3US$m−3 against 0.6US$ m−3 for the HR-flotation process. Results found were proved to be similar to those foundin recent ADM treatment installations in South Brazil. The quality of the treated water is fairly good, nearlyfree of heavy metals ion, low BOD (biological oxygen demand) and TOC (total organic content), low solidscontent and may be readily reused for irrigation, industrial processes and as wash water (among others,streets, vehicles, dust control). However, there is a need to extend the use of this treated water resource, butthis, at least in Brazil, has not been legislated properly. It is concluded that this research will contribute in thediscussion of this old and complex problem in acid mining effluents worldwide.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

Natural drainage or subterranean flows pass through surface anddeep mine coal mining activities and are commonly contaminated bymetals ions and by a low pH. These AMD's (Acid Mine Drainage)eventually migrate into streams and rivers and impact negatively onthe quality of these water bodies.

Conventional AMD treatment techniques are combinations ofneutralization and precipitation (usually with lime), followed bysettling of the precipitates in ponds (Kontopoulos, 1998). In manycases, this technology either does not work well, or the systems arenot maintained (uncovered sites). Others, especially when the AMD isnot heavily loaded, the volume is small or when the flow-rate is low,its treatment may include peroxide oxidation, reverse osmosis, ionsexchange and adsorption. Some techniques are expensive, whileothers have low efficiencies and/or do not withstand acid water.

+55 51 33089477.r (A.N. da Silveira),io).

l rights reserved.

AMD treatments from coal mines using neutralization and solid/liquid separation by dissolved air flotation-DAF are now in progress inthe USA and Brazil (Ross et al., 2003; Rodrigues and Rubio, 2007). TheDissolved Air Flotation (DAF) is a proved and well-known technologyused to separate suspended solids, fibers and dispersed oils fromwater.Bubbles are formed by a reduction in pressure of water pre-saturatedwith air at pressures higher than atmospheric (3 to 6 atm) (Rubio et al.,2002). The supersaturated water is forced through needle-valves,venturi or special-orifices, and clouds of bubbles, 30–100 µm indiameter, are produced just down-stream, feeding the flotation cell.

In 1999, in the USA (Ross et al., 2003) a DAF systemwas integratedto an AMD treatment system to provide an adequate stream prior todischarging into a local stream. These authors found 87% of the metalswere removed. The flow rate of DAF was about 80 m3 h−1, and systemoccupied an area of 17 m2. The unit (4.5 m h−1 loading capacity), waspreceded by a flashmix tank for pH control followed by a flocmix tankfor polymer flocculation. This system has been in operation since 1999and has kept the site's owners in compliancewith state regulations fortheir discharge. Thus, concentrations of iron, manganese, andaluminum were reduced by 87–89% by the DAF system and thedischarged pHwas raised from a pH of approximately 3 to a pH of 7–9,which was well within permitted limits.

Table 1Examples of lamella settler applications in AMD treatment.

Year, Place References Observations

2002–2003,Nevada–California,

USA

Bates, E.; Mayer, K.; Thun, R.; Booth, R.Active and Semi-Passive LimeTreatment of Acid Mine Drainage atLeviathan Mine. Cincinnati, Ohio.p. 1–8. 2006

1.3 kg of lime/1000L ofAMD - RemovalN99% forall metal ions studied(except lead=75%)

1990, USA Professional Chemical TechnologyInternational, Inc. Company Profile.Technical applications bulletins

Final turbidity=0.5 NTU;Flow rate=113 m3 h−1

2000, Cornwall,England

Bone, B. Remediation schemes tomitigate the impacts of abandonedmines. Environment agency forEngland and Wales, 2003

Sludge density=20% w/w; Flow rate=720 m3 h−1; 145tmonth−1 of heavymetals ions removed(efficiency 99.2%)

Fig. 1. AMD flow rates values between 2003 and 2007.

104 A.N. da Silveira et al. / Int. J. Miner. Process. 93 (2009) 103–109

In Brazil, the first AMD flotation treatment plant corresponded to avery small unit (10–15 m3/h) treating AMD generated in a coal em-barkation site. This unit uses lime, sodiumoleate to generate the bubblesand to make particles hydrophobic and a polyacrylamide to form theflocs to be floated (Menezes et al., 2004; Rubio et al., 2007a,b). Herein,this “fresh” AMD, formed after rain water penetration through thestockpile, is neutralized with lime and the resulting precipitates arehydrophobized with sodium oleate before flotationwith microbubbles.Should the solids content rise, as in a heavy loaded AMD, the DAFrecycling ratio has to be increase over 40%, this “lifting power” problemis one of the drawbacks of this microbubbles flotation process.

Lamellar settling (LS) of flocs is another solid–liquid separationalternative employed for the treatment of Acid Mine Drainage. Someapplications have been reported in the last ten years. Bates et al.(2006) and Bone (2003), claim the successful of removal values ofmore than 95% of the feed metal ions. Main characteristics of thesestudies are shown in Table 1.

The introduction of horizontal plates in a conventional settler wasreported by Hazen in 1904 (apud Di Bernardo and Dantas, 2005) toenhance the effective area of the sedimentation tanks. However thedesign presented some difficulties in collecting the decanted sludge.The introduction of inclined plates with high elevation withinconventional tanks (Culp et al., 1968, 1969), i.e. a lamella settler, wasan advance in water and effluent treatment systems resulting in thecompact construction of sedimentation tanks (small foot print).

Thus, lamella settler consists of inclined plates that can be adjustedfrom 45 to 60°, where solids can be most effectively decantedmaximizing the available settling area (Carvalho, 1998; Demir, 1995;Ziolo, 1996). It performs the same function as a conventional clarifierbut it occupies only a fraction of the space. The effective settling area isequal to a projected area of each plate multiplied by the number ofplates (Leung and Probstein,1983; Soriente and Gurnari,1989). Hence,the area and costs involved can be reduced by matching the clarifyingand thickening requirements more closely.

Table 2Acid Mine Drainage (SS-16 site), main parameters.

Parameter Acid water

pH 3.0SO4

−2, mgL−1 800±20Mn, mgL−1 2.1Fe, mgL−1 3.0Al, mgL−1 33.7Ca, mgL−1 66Total solids (TTS), mgL−1 1279Total dissolved solids (TDS), mgL−1 974Turbidity, NTU 0.32Color, Hz 19Conductivity, µScm−1 1153Hardness, mg L−1 250

This work is a continuation of a series of papers on development,studies of the mechanisms involved and applications of advancedflocculation followed by flocs flotation and/or flocs settling. The aims ofthis work were to generate two types of flocs, aerated or not, employingthe FGR® (Rubio and Carissimi, 2005) and evaluates two different flocs-liquid separation techniques. More, this work contributes to the localdiscussion on which AMD treatment process would be more suitable,efficient and cheaper. Two recent installation of about 250 m3h−1 havecommissioned, one employing DAF and a second lamellar settling(Rubio et al., 2007a,b; Da Rosa, personal communication, 2009).

2. Materials and methods

2.1. Materials and reagents

AMD. This acid effluent (a drainage from an abandoned coal mine)is composedmainly of Fe, Al andMn ions (Table 2), pH 3±0.5 and theflow rate (Fig. 1) varies from 60–90 m3 h−1 (85 m3 h−1, the meanvalue). Table 2 shows averaged values included Ca ions as suggested.The monitored volume flow rate, between 2003 and 2007, is shown inFig. 1.

Lime was employed for the AMD neutralization and metal ionsprecipitation and Flonex 9045 (a high molecular weight cationicpolymer supplied by SNF/Floerger®) was utilized to generate flocs. Inthe flotation studies, sodium oleate was employed to enhance theflocs hydrophobicity and process kinetic. All reagents were used as

Fig. 2. FGR® - the Flocs-Generated Reactor (Rubio and Carissimi, 2005).

Table 3Experimental operating parameters for the flotation and lamella settling pilot studies.

Processes Parameters (operating) Values

Neutralization/precipitation Tank volume 2000LMechanical agitator 1500WResidence time (conditioning) 30 min

Flocs formation - FGR Number of rings 19Diameter of pipe 0.025 mLength 12 mVolume 5.9×10−3m3

Residence time 0.3 minVelocity Gradient, G 1000 s−1

Flotation Cell Volume 160LResidence time 9.6 minSuperficial liquid velocity 9 m3 m−2 h−1

Air flow rate 0.3 m3 h−1

Area 0.11 m2

Lamellar settling Tank volume 330LResidence time 19 minSuperficial liquid velocity 4.5 m3 m−2 h−1

Area 0.22 m2

Inclination of the tubes 60°Diameter of the tubes 0.05 m

Table 4Treatment of AMD: description of the studies sequence.

Month Processes

Flotation Lamellar settling

1 F1 S12 F2 S23 F3 S34 F4 S45 F5 –

6 F6 S57 F7 –

8 F8 S6

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commercial products and solutions were prepared with local tapwater.

2.2. Equipment and procedures

Flocculation of precipitates was carried out in a special flocculator,FGR® (Rubio and Carissimi, 2005) (see Fig. 2). The FGR has been

Fig. 3. Flotation (high rate) pilot plant unit for AMD treatment (~1 m3h−1). Conditions [1precipitation; [4] FGR (flocs generator reactor); [5] Needle valves for bubble formation; [6][7] MB (micro-bubbles) - HR (high rate)-flotation unit.

studied, in detail, in several projects in the last years in Brazil(Carissimi, 2007; Rubio et al., 2007a). The FGR design has followed themodel studied by Carissimi (2007), using velocity gradient (G value)of about 1000 s−1 to ensure good flocculant dispersion and flocsgrowing. Main characteristics and advantages of this in-line mixingreactor over agitated tanks are: no moving parts; plug flow (less shortcircuits and dead zones); low volume/retention times and low foot-print (Rubio and Carissimi, 2005; Carissimi, 2007).

Herein, the reactor had a capacity of about 1.2 m3 h−1 (20 Lmin−1),made of industrial flexible PVC pipe (model Spiraflex, Goodyear®brand). The reactor's constructive characteristics and residence time,together with other equipment used are shown in Table 3.

High Rate Flotation (HRF) and lamella settling (LS) studies wereconducted at room temperature over a period of 8 months, coveringsummer and winter. The flow exiting from the LS and HRF wascollected in tanks. Samples were collected (composites of at least 6hours) for determining metal ions concentrations (duplicates). Usingatomic absorption (SpectrAA 110, Varian®). All samples werepreserved following directions from Standard Methods for theExamination of Water and Wastewater (APHA, 2005. The identifica-tion of each of those runs (6–8months) is shown in Table 4.

2.2.1. Removal of heavy metals ions by flotationThis work was conducted in a small pilot unit treating about 1–1.5

m3h−1 (Fig. 3) with the feed being collected into two 2 m3fill tanks.

Lime (250mgL−1) was added for neutralization (pH 9) andmetals ionsprecipitation, in the form of hydroxides. Then, 5 mg L−1 (300gt−1)flocculant (a cationic high molecular weight polyacrylamide) and15 mgL−1 (300gt−1) sodiumoleatewere addedbefore feeding the FGR.

The HRF-High Rate Flotation has an effective volume of 0.15 m3

and a multiphase centrifugal pump (water/air), Edur® (Fig. 4), wasemployed to disperse, dissolve and saturate air in water. The pumpreceives the air at the inlet (suction), shears it within the impeller andrapidly reaches an operating pressure of about 8kgf cm−2 (784kPa).

The air saturated water flows downstream through a connectingtubepassing througha1 inchneedle valvewheredepressurization takesplace to formmicrobubbles bycavitation andnucleation of the dissolvedair. Studies reported (at similar conditions) byRodrigues (2004) showedthat bubbles had diameters smaller than 200 μm (Fig. 5).

The HRF has inclined lamellae in the collection zone to enhance theaggregatesfloating “bed” stabilityandfluidization (Fig. 6). In the bottom

] lime; [2] reagents (flocculants and collector); [3] AMD neutralization – metals ionsmultistage (three phase) pump for in line, air-water saturation, air compressor pump;

Fig. 4. Centrifugal multiphase (water/air) pump (Edur®) employed to disperse, dissolveand saturate air in water.

Fig. 6. Flotation (high rate) unit. Detail of the inclined lamellas inside the flotation tankto enhance floc-flotation recovery.

106 A.N. da Silveira et al. / Int. J. Miner. Process. 93 (2009) 103–109

of this flotation cell, where the treated AMD exits the unit, a speciallydesigned porous platewas introduced to allow the treatedwater toflow,in the laminar hydrodynamic regimen (higher rate) (Fig. 7).

A fraction of the clarified water was recycled and saturated in theEdur pump and microbubbles were generated and introduced in theHRF cell. Flow feed ratewas fixed at about 1–1.3 m3h−1 and the recyclerates studied were 20, 30, 40 and 50%. A 30% of this ratio was found tobe the optimal, while keeping the saturation pressure at 8kgf cm−2.

Process efficiency was evaluated measuring water turbidity (Hachmodel 2100 N) and apparent color (Merck model SQ 118). Otheranalyses followed the Standard Methods for Water and WastewaterExamination (APHA, 2005).

2.2.2. Removal of heavy metals ions by flocculation-settling.Studies of lamellar settling were conducted at pH 9, using the same

reagents without flotation collector: 250 mg L−1 of lime, 5 mg.L−1 ofFlonex and 1 m3 h−1 feed flow rate. Figs. 8 and 9 show details of the LSrig and lamellae employed.

3. Results and discussion

3.1. Removal of heavy metals ions

Figs. 10–12 show results of Fe, Al and Mn ions removal at pH 9using separation of flocs by either lamellar settling or flotation. Allresults show high and similar efficiencies reaching removal rateshigher than 90% for all metal ions studied. At pH, values closer to 9.0,

Fig. 5. Bubble size distribution, generated by the multiphase Edur® pump, adapted fromRodrigues (2004), from our laboratory. 8 kgf.cm-2–784 kPa.

manganese ions precipitate as manganese hydroxide, Mn (OH)2allowing its removal. Fig.13 shows a species diagram, constructed for a1.82 mM of Mn+2 aqueous solution systems.

Results obtained (over 6–8 months) showed that removal of ions(in all cases) was independent of the separation process, whether HR-flotation or LS. Ions concentrations, in the treated water, were alwayssmaller than those of emission standards.

Regarding calcium removal by DAF this does not occurred due to thefact that calcium ions, added at the neutralization stage, do not formfloatable insoluble calcium hydroxides species at pH 9 (a high pH isrequired). Yet, this is not a problem for the quality of the treated water.

In the flotation study, the very light “aerated flocs”, which wereformed within seconds, had very high up-rising rates (N120mh−1)allowing a rapid solid–liquid separation (Rubio et al., 2007b). Notmany papers have been published on the formation and characteriza-tion of these special flocs because they are difficult to obtain (Rubioand Carissimi, 2005; Rubio et al., 2007b). In this work, aerated flocswere formed in the RGF® after particles (flocs) enter into contactwith microbubbles under high shearing. Main characteristics andadvantages of this in-line mixing facilities compared to agitated tanksare: no need for moving parts; plug flow (less short circuits and deadzones); low volume/retention times (Camp-number − Ca), low foot-print (Rubio and Carissimi, 2005; Rubio et al., 2007b) and easy todesign for different effluent flow-rates.

Because of rapid formation of the aerated flocs, the loading ca-pacity of the treatment unit is as high as 13–15 mh−1 showing a highpotential to treat (if needed) effluents at a high rate. Moreover, withthe elements of this advanced HR-flotation cell, lamellae kept thefloated flocs in a floating bed which avoided floc settling. The porousplate allowed for rapid water drain off the cell.

Fig. 7. Flotation (high rate) unit. Detail of the porous plate at the bottom of the tankallowing a smooth flow of the treated water at the outlet (in a laminar hydrodynamicregime).

Fig. 8. Lamella settler unit (~1–1.3 m3h\−1) for AMD treatment: [1] LS (lamella settler-with inside tubes); [2] Sludge; [3] Treated water to reuse; [4] Pump; [5] FGR (Flocs ReactorGenerator).

Fig. 9. (a) Inclined tubes introduced in the lamella settler; (b) Photograph of the lamella settler unit.

107A.N. da Silveira et al. / Int. J. Miner. Process. 93 (2009) 103–109

In the absence of microbubbles, the lamellar settling of non-aerated flocs was also rapid and the settling rates of about 5–6 m h−1

were obtained. The FGR produced dense and uniform flocs with astrength which withstood high shearing. Separations by lamellarsettling occurred rapidly because of the compact flocs which formed.

Fig. 10. AMD treatment by neutralization and flocs-HR (high rate)-flotation (tests series Fbetween Fe concentrations in AMD feed (initial), treated water ion and emission standard

LS showed to be easier to operate compared to flotation and has someeconomical advantages due to reagents' savings (no need of acollector) and lower energy consumption. The estimate of operatingcosts using LS, at pH 9, is about 0.3 US American dollar per m−3 (US$m−3 0.6 for HRF). These operating costs have shown to be fairly close

) or LS-lamellar settling (tests series S) of flocs, at pH 9 (iron removal): Comparisonslimits (Brazil). Conditions: see Tables 2–4.

Fig. 11. AMD treatment by neutralization and flocs-HR (high rate)-flotation (tests series F) or LS-lamellar settling (tests series S) of flocs, at pH 9 (aluminum removal): Comparisonsbetween Al concentrations in AMD feed (initial), treated water ion and emission standard limits (Brazil). Conditions: see Tables 2–4.

Fig. 12. AMD treatment by neutralization and flocs-HR (high rate)-flotation (tests series F) or LS-lamellar settling (tests series S) of flocs, at pH 9 (manganese removal): Comparisonsbetween Mn concentrations in AMD feed (initial), treated water ion and emission standard limits (Brazil). Conditions: see Tables 2–4.

Table 5Comparative results between emission standards (reuse in irrigation) and AMD treatedquality (HRF or LS).

Parameters Averaged values EPA⁎ (Quality SABESP ⁎⁎(Brazil)

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to those found in the two recent AMD industrial installations in theregion (Da Rosa, personal communication, 2009). Herein, the sludgeproduced either by both flotation or settling contains 1–2% solids(weight basis) or 1.5 kg h−1. Sludge is dried in covered open air bedswhere the water drains off in residence timesN8–10 days. Driedsludge is being utilized as filler in the local ceramic industry.

Moreover, DAF application for the separation of precipitatesformed in loaded (very acid) AMD and metal ions concentrations(about 3000 mg L−1) has been proved to be less effective than dilutedones (Da Rosa, personal communication, 2009). It is believed that thisis because of the heavier, bigger and numerous flocs to be floatedwhich make the air (microbubbles)-to-solids ratio very low andincapable to sustain the denser flocs. Further, it has been observedthat the generation of bubbles becomes very much affected by thehigh concentrations of ions in these AMD (surface tension above

Fig. 13. Chemical diagram species, constructed for manganese aqueous solution.Co: 1.82 mM Mn+2.

75 mS cm−1) requiring the use of surfactants for an effective aircavitation and nucleation at the needle valve (unpublished studies).

3.2. Reuse of water

Table 5 shows the potential uses for the treated water. The treatedwater from this process can be readily reused because of the lowconcentrations of inorganic ions, solids, BOD, Fecal coliforms and TOC.

(LS or HRF)-This work

standardto irrigation)

pH 9 6–9 6–9SO4

2−, mg L−1 700 – –

Mn, mg L−1 0.4 10 –

Fe, mg L−1 0.2 20 –

Al, mg L−1 3 20 –

Ca, mg L−1 200 – –

TS, mg L−1 950 – –

TDS, mg L−1 920 500–2000 –

Turbidity, NTU 2.5 2* b15Color, Hazen 10 – –

Conductivity, µS cm−1 1100 – –

BOD, mg L−1 N.D.⁎⁎⁎ ≤10 b30Fecal coliforms, NPM/100 mL N.D. N.D. b200TOC, mg L−1 0.8 – –

Surface tension, mN m−1 70 – –

Hardness, mg L−1 de CaCO3 600 – –

Conditions: [lime]=250 mg L−1; pH 9 (initial pH=3), [Flonex 9045]=5 mg L−1.⁎ EPA. Guidelines for water reuse. U.S. Environmental Protection Agency,

Municipal Support Division, Washington, DC, EPA/625/R-04/108, 449 pages, 2004.Food crops, without processing.

⁎⁎ Available in www.sabesp.com.br. Sabesp — Companhia de Saneamento Básicodo Estado de São Paulo. Date: 04/10/2007.

⁎⁎⁎ N.D.: Not detected.

Table 6Alternatives for the reuse of the treated AMD water.

Alternatives for waterreuse

Possible applications

Urban Landscape irrigation, wash waters (streets and vehicles),dust depression, fire protection

Agricultural andforestry purposes

Agricultural production and culture of planted forests

Environmental purposes Environmental recovery (dilution)Industrial purposes Industrial water usage (various)Aquaculture Animal farms or aquatic vegetable culture

109A.N. da Silveira et al. / Int. J. Miner. Process. 93 (2009) 103–109

There is no legislation in Brazil regarding the reuse of industrialtreated water. Table 5 shows comparative values for treated water(HRF or LS) with suggested EPA and SABESP limits for water reuse inirrigation purposes (Table 6). Only sulfate ions are present in fairlyhigh concentrations, limiting recycling alternatives, this being thepresent challenge in our research group. A plant to treat the SS-16AMD water is currently being constructed and its design followed theloading capacities proved in this work. The water treated will be usedto clean pavements, streets and vehicles as well as for irrigation anddust control.

4. Conclusions

This work showed comparative results for the treatment of anAMD, after heavy metal ions precipitation, flocculation and solids(flocs)/liquid separation. Results obtained show that either flotation(high rate flotation-HRF) or lamellar settling (LS) presented similarefficiencies for the flocs and removal of heavy metals ions at pH 9.Both units were very compact units and take advantages of the veryrapid flocculation attained in the FRG® in the presence or absence ofmicrobubbles. In the presence of microbubbles the up-rising velocitiesof the flocs (aerated) were very high and without bubbles the flocswere heavy and settled readily. This led to rapid flocs/liquid separationby flotation (13 m h−1 superficial loading capacity). Solids werecollected using an advanced flotation cell design to keep the flocs onthe top of the cell and optimizing the water outlet off the tank. Thus,against for LS were obtained. The maximum loading capacity bylamellar settling was lower (5–6 m h−1) but this technique showedlower energy consumption and does not require a flotation collector.The good quality of the treated AMD water, heavy metals free, lowBOD, low TOC, among others, allows a possible recycle for varioususes. It is believed that both separation techniques have high potentialfor treating AMD and water reuse.

Acknowledgements

The authors wish to thank students and colleagues from LTM-Universidade Federal do Rio Grande do Sul and to all institutions

supporting research in Brazil. Special thanks to SIECESC and Aquaflotfor technical and financial assistance.

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