Arsenic Removal from Mine Tailings for Recycling via Flotation

Junhyun Choi1, Kyuhyeong Park1, Jeongsik Hong1, Jayhyun Park2 and Hyunjung Kim1,+

1Department of Mineral Resources and Energy Engineering, Chonbuk National University,664-14 Duckjin-dong 1Ga, Duckjin-gu, Jeonju, Jeonbuk 556-756, Republic of Korea2R&D Team, Institute of Mine Reclamation Coporation, Coal Center,30 Chungjun-dong, Jongno-gu, Seoul 110-727, Republic of Korea

In this study, we propose a flotation process to remove the arsenic from Samkwang mine tailings in South Korea, which contained a higharsenic content, in order to render them suitable for recycling. In order to maximize the arsenic removal from the mine tailings, three variables(type of collectors and activators, and solution pH) were systematically investigated. Characterization experiments (X-ray diffraction andelectrokinetic property analyses) were carried out to complement the flotation results, and the results showed that the mine tailings were mainlycomposed of arsenopyrite (FeAsS), arsenic trioxide (As2O3, As4O6), arsenic pentoxide (As2O5) and quartz (SiO2). The flotation results obtainedusing different collectors (i.e., potassium amyl xanthate (PAX), sodium oleate, sodium dodecyl sulfate) revealed that arsenic removal efficiencywas greatest in the presence of PAX, which was explained by the difference in the electrokinetic properties and the interaction type of collectorswith arsenic-bearing minerals. Meanwhile, the addition of activators (Na2S, CuSO4, Na2S+CuSO4) and the pulp pH significantly affected thearsenic removal efficiency. The arsenic removal was maximized in the presence of mixed activators (Na2S+CuSO4) at low pH. The effect ofactivator type and pulp pH on the arsenic removal efficiency was attributed to the coupled role of the sulphidization of arsenic oxides (e.g.,AS2O3, AS4O6 and AS2O5), the activation of sulphidized minerals, and the formation of dixanthogen. Lastly, based on the results obtained fromthe parameter optimization tests (i.e., type of collector and activator, and pulp pH), a series of flotation processes consisting of rougher flotationand two subsequent scavenging flotations was designed. The results demonstrated the capability of the process to successfully remove arsenicfrom Samkwang mine tailings for recycling. [doi:10.2320/matertrans.M2013285]

(Received July 25, 2013; Accepted October 7, 2013; Published November 15, 2013)

Keywords: mine tailings, arsenic removal, flotation, recycling

1. Introduction

Arsenic is one of the most dangerous inorganic pollutants,causing health and environmental emergencies in severalareas of the world. Exposure to arsenic causes serious humanhealth problems including irritation of the stomach andintestines and, especially, an increased risk of developinglung, liver, kidney and skin cancer.1­6) In addition, arsenicfrom mine tailings has caused the serious contamination ofsoil, surface water and groundwater.7­10)

Arsenopyrite (FeAsS) is one of the most common arsenic-bearing minerals and is found in a range of ore deposits, in-cluding magmatic, hydrothermal and porphyry-style systems.Due to its common association with gold, FeAsS is oftenmined.11,12) In South Korea, in order to obtain gold, a lot ofcyanide was conventionally used as a depressant during theflotation process at gold-containing mines because cyanideacts as an inhibitor for the electrochemical reactions onthe surface of the FeAsS. In the presence of cyanide, theadsorption of xanthate onto FeAsS was significantlyinhibited.13­15) This historical use of a lot of cyanide hasbeen reported to have resulted in many South Korean minetailings with high arsenic contents.16­18) The mine tailings ofthe approximately 1000 dormant and/or abandoned minesin South Korea are a threat to the natural environment andnational health.

The Korean government has initiated restorations of thedormant and/or abandoned mines. One of the major methodsused in South Korea to prevent soil pollution/contaminationincludes the establishment of concrete-retaining walls forpreventing loss of mine tailings and mine-waste prior to soil

covering.19) This method of establishing preventive structuresis effective for restricting the physical movement oftailing particles; however, the method still suffers a risk ofenvironmental pollution of the surrounding areas of the minesby the infiltration of rainfall through the mine tailings (e.g.,acid mine drainage), indicating that alternative methods arerequired to reduce the risk. Much research has been devotedto developing a flotation method capable of separatingarsenic-bearing minerals.20­25) For instance, some studies20,22)

reported the flotation technique by using thionalide as acollector for the selective enrichment of arsenic. In addition,Bruckard and the colleagues21) investigated the flotationbehavior of arsenic as a function of pulp pH. More recently,there was an attempt to develop an environmentally friendlyflotation process for the selective separation of arsenic.25)

Nevertheless, no attempt to investigate arsenic removal frommine tailings through flotation has been made in SouthKorea. Therefore, considering the regional diversity of minetailings in terms of physicochemical and mineralogicalcharacteristics, relevant studies are required.

According to Korea Soil Standard Criteria, the warninglevel for arsenic concentration is 50mg/kg for zone 2 areas,which include forest land, salt farm and waterfields.26,27)

In this study, therefore, flotation was conducted to recycleSamkwang mine tailings in South Korea containing a higharsenic content (target arsenic concentration at the tailingsafter flotation ¯50mg/kg). The content of other heavymetals (i.e., cadmium, chromium, copper, lead, zinc) wasalmost equal to or less than the warning level for zone 2 areas(Table 1).26,27) Furthermore, with the Korea government’sgoal of minimizing the loss of mine tailings, the effects ofcollectors, activators, mixed activators, and solution pH werealso examined.+Corresponding author, E-mail: kshjkim@jbnu.ac.kr

Materials Transactions, Vol. 54, No. 12 (2013) pp. 2291 to 2296©2013 The Japan Institute of Metals and Materials EXPRESS REGULAR ARTICLE

2. Materials and Methods

2.1 SamplesSamkwang mine tailings containing high arsenic and pure

FeAsS which was obtained from Industry & Trade Co.(China) were selected for the present study. For thecharacterization and flotation experiments, the tailings weresieved between ¹65 mesh and +200 mesh (212­75 µm,Tyler Standard), collected, and used in flotation tests. Toinvestigate the chemical composition and mineralogy ofthe raw tailings, inductively coupled plasma (ICP) analysis(Optima 5300PV, PerkinElmer Inc., USA) and X-raydiffraction (XRD) analysis (D/Max-2200/PC, Rigaku,Japan) were conducted, respectively.

2.2 ReagentsThe xanthate used in this study was potassium amyl

xanthate (PAX, C5H11OCS2K) having a purity of 90% orhigher and made by Hong Yuan Industry & Trade Co. inChina. Sodium oleate (SO, C18H33O2Na) and sodium dodecylsulfate (SDS, CH3(CH2)11OSO3Na) were employed as othercollectors and obtained from Sigma-Aldrich. Sodium sulfide(Na2S) and copper sulfate (CuSO4) manufactured by Sigma-Aldrich were used as activators. Aerofloat-65 (AF-65,CH3(C3H6O)4OH) supplied by American Cyanamid, USAwas used as a frother and analytical grade of HCl and NaOH(Fisher Scientific) were used as pH modifiers.

2.3 Electrokinetic properties of the Samkwang minetailings

The electrophoretic mobility of the Samkwang minetailings and pure FeAsS was measured at different pHconditions using a zeta-potential analyzer (ELS-Z, Otsuka,Hirakata, Japan). To measure the mobility, the samples wereground using a mortar. Then, 1 g of each sample was addedto DI water (Milli-Q Plus, Millipore Ltd., UK) and theelectrophoretic mobility of the samples was measured atdifferent pH conditions. The measured mobility valueswere converted to zeta potentials based on Smoluchowskiequation.28,29) The solution pH was adjusted with 1N HCland NaOH by a pH meter (Accumet AP61, Fisher Scientific),and the measurements were conducted in triplicate.

2.4 Flotation testsFor flotation experiments, a 1 L flotation cell (Denver

Sub-A, USA) was used. In every test, 200 g Samkwang minetailings, 800mL deionized (DI) water, impeller speed of1000 rpm and flotation time of 10min were applied. Inaddition, the AF-65 (250mL/ton) was conditioned for 3minfor all experiments before the air was introduced in thesuspension. In the first set of experiments, to select thedesired type of collectors, SO, SDS or PAX was added to the

pulp in the same concentration (100 g/ton) and then wasconditioned for 5min, followed by 3min frother conditioningand 10min flotation. For the second set of experiments,Na2S or CuSO4 (50­200 g/ton) was added to examine theeffect of activators and determine their optimum concen-tration to maximize arsenic removal efficiency, followedby 5min collector conditioning, 3min frother conditioningand 10min flotation. For the third set of experiments, thedesired concentration of mixed Na2S and CuSO4 was addedto the pulp at two different pH conditions (pH 4 and 9)to further examine the coupled effect of mixed activatorsand improve arsenic removal efficiency, followed by 5mincollector conditioning, 3min frother conditioning, and 10minflotation. Lastly, in order to obtain recyclable products witha target arsenic concentration after flotation of less than50mg/kg, two subsequent scavenging processes were carriedout at the optimum conditions (i.e., desired collector’s typeand activators’ concentration, and solution pH) as determinedfrom the previous sets of experiments. The floated andunfloated products were collected, filtered with a 0.45 µmfilter (ADVANTEC, Toyo RoshiKaisha, Japan) using a smallvacuum pump, and dried at 80°C in an oven. The arsenicremoval efficiency was calculated by ((Cc)/(Ff )) © 100.Where, C and F denote the weight of the concentrate (i.e.,floated product) and the feed, respectively. And, c and fdenote the arsenic concentration (i.e., assay) of the concen-trate and the feed, respectively.

3. Results and Discussion

3.1 Physicochemical properties of the Samkwang minetailings and pure arsenopyrite

The XRD patterns and ICP analysis results for theSamkwang mine tailings are presented in Fig. 1 and Table 1,respectively. The arsenic, cadmium, chromium, copper, leadand zinc contents in the tailings measured through ICP wereabout 8138, 20, 68, 22, 29 and 607mg/kg, respectively,which indicated that arsenic is the main contaminant(Table 1). The XRD analysis revealed the main minerals tobe FeAsS, arsenic trioxide (As2O3, As4O6), arsenic pentoxide(As2O5) and quartz (SiO2) (Fig. 1). Since arsenic was presentin the forms of FeAsS, AS2O3, AS2O5 and AS4O6 (Fig. 1),the tailings were considered suitable for using flotation for

Fig. 1 XRD patterns of the Samkwang mine tailings.

Table 1 Heavy metal composition of the Samkwang mine tailings.

Chemical composition (mg/kg)

As Cd Cr Cu Pb Zn

8137.8 19.58 68.15 21.68 29.35 606.83

J. Choi, K. Park, J. Hong, J. Park and H. Kim2292

arsenic removal. Figure 2 shows the zeta potentials of thetailings and pure FeAsS according to pH. The isoelectricpoint (IEP) of pure FeAsS ranged from 4 to 5, which isconsistent with the results from a previous study.31) The IEPof the tailings was determined to be less than 2, which wasattributed to the large fraction of SiO2 present in the tailings,as indicated in the XRD results (Fig. 1).30)

3.2 Arsenic flotation3.2.1 Effect of collectors

In order to investigate the effect of collectors on theflotation of the Samkwang mine tailings and further select theoptimum reagent for the subsequent processes, flotationexperiments in accordance with PAX, SO and SDS were firstcarried out at an adjusted pulp pH of 9 and the results arepresented in Fig. 3. The arsenic concentration of the tailswas about 8125 and 15030mg/kg and the arsenic removalefficiency was about 3.77 and 2.95% when SO and SDSwere used as the collector, respectively. The interaction ofanionic surfactants such as SO and SDS with FeAsS wasexpected to be unfavorable, due to the electrostatic repulsiveforce between anionic surfactants and FeAsS, at pH 9because the IEP of FeAsS ranged between 4 and 5(Fig. 2).30) Therefore, FeAsS did not float well using SOand SDS at pH 9. Meanwhile, when PAX was used as acollector, the arsenic concentration of the tails was about

6678mg/kg and the arsenic removal efficiency was about29.06%, indicating that xanthate was a more powerfulcollector for FeAsS flotation. Chemisorption has beensuggested as the adsorption mechanism of xanthate ions(X¹) onto the surface of sulfide minerals, whereas the twoother collectors (SDS and SO) were physically adsorbed ontothe mineral surfaces.32,33) More specifically, the oxidationof xanthate ions (X¹) to dixanthogen (X2) occurs onto thesurface of the FeAsS which acts as a catalyst for theoxidation/reduction reaction.33,34) This process renders thesurface of FeAsS hydrophobic. In fact, previous studiesreported that FeAsS floated well using xanthate as acollector.35­38) Hence, PAX was utilized as the collector inthe following experiments.3.2.2 Effect of activators

Figures 4 and 5 show that arsenic concentration of thetails and the arsenic removal efficiency after the flotationin accordance with the addition of Na2S and CuSO4 asactivators, respectively. Overall, the addition of Na2S andCuSO4 before PAX addition (100 g/ton) strongly affectedthe arsenic concentration of the tails and the arsenicremoval efficiency, which were about 4679, 4793, 4080and 4681mg/kg and 52.39, 51.42, 58.73 and 68.67% in thepresence of 50, 100, 150 and 200 g/ton Na2S, respectively

Fig. 2 Zeta potentials of pure FeAsS and the Samkwang mine tailings atdifferent solution pHs.

Fig. 3 Arsenic concentration of the tails and arsenic removal efficiencyafter flotation. The experiments were carried out at pH 9 with PAX, SOand SDS concentrations of 100 g/ton and AF-65 concentration of250mL/ton.

Fig. 4 Arsenic concentration of the tails and arsenic removal efficiencyafter flotation. The experiments were carried out at pH 9 with Na2Sconcentration of 50­200 g/ton, PAX concentration of 100 g/ton, andAF-65 concentration of 250mL/ton.

Fig. 5 Arsenic concentration of the tails and arsenic removal efficiencyafter flotation. The experiments were carried out at pH 9 with CuSO4

concentration of 50­200 g/ton, PAX concentration of 100 g/ton, and AF-65 concentration of 250mL/ton.

Arsenic Removal from Mine Tailings for Recycling via Flotation 2293

(Fig. 4). The arsenic removal tended to increase withincreasing Na2S addition. Additionally, the arsenic concen-tration of the tails was approximately 1996mg/kg lower andthe arsenic removal efficiency was about 39.31% greater inthe presence of Na2S compared to in the case of its absence.The Na2S-induced enhancement in arsenic removal wasattributed to the sulphidization of the arsenic oxides suchas AS2O3, AS4O6 and AS2O5 by Na2S, which led to moreselective interaction between the surface of the sulphidizedarsenic oxides and xanthate.35) Specifically, soluble sulfideions (S2¹) could form a sulfide layer onto the surface ofthe arsenic oxides, which favors xanthate adsorption ontothe sulphidized arsenic oxides.39­41) The addition of CuSO4

before PAX addition also strongly affected the arsenicflotation (Fig. 5). In the presence of 50, 100, 150, 200 g/tonCuSO4, the arsenic concentration of the tails and the arsenicremoval efficiency were about 3210, 3869, 3833 and3110mg/kg and 69.4, 62.47, 71.21 and 77.06%, respectively.The trend for the arsenic concentration of the tails and thearsenic removal efficiency in the presence of CuSO4 wassimilar with that for Na2S, showing the maximum arsenicremoval at the highest CuSO4 dosage of 200 g/ton.Specifically, the arsenic concentration of the tails was about3568mg/kg lower and the arsenic removal efficiency 47.7%greater in the presence of CuSO4, as compared to the casewithout CuSO4. Previous studies reported that cupric ions(Cu2+) could activate sulfide minerals and enhance theirflotation with xanthate.42,43) Wang et al.44) reported that Cu2+

could form copper complexes onto the surface of FeAsS dueto their strong electron accepting ability through which theadsorption of xanthate ions (X¹) onto the surface of FeAsSwas enhanced. Although arsenic removal maximized in thepresence of 200 g/ton Na2S or CuSO4, the arsenic concen-tration in tails did not meet the warning criteria (50mg/kg)for recycling. Since the main purpose of this study was torender the Samkwang mine tailings suitable for recycling,we conducted additional flotation tests with 200 g/ton ofboth Na2S and CuSO4 at different pH conditions (pH 4versus pH 9) to improve the removal efficiency.3.2.3 Effect of mixed activators

Figure 6 shows the arsenic concentration of the tails andthe arsenic removal efficiency after the flotation in thepresence of mixed activators (200 g/ton Na2S + 200 g/tonCuSO4) at two different pH conditions (pH 4 and 9).Overall, the arsenic concentration of the tails and the arsenicremoval efficiency were lower and greater, respectively,in the presence of mixed activators (200 g/ton Na2S +200 g/ton CuSO4) than in the case of their individual use(i.e., 200 g/ton Na2S or 200 g/ton CuSO4) at pH 9. At pH 9,the arsenic concentration of the tails and the arsenic removalefficiency in the presence of both Na2S and CuSO4 wereabout 2933mg/kg and 80.11%, respectively, which werearound 1748mg/kg lower and about 11.44% greater than inthe case of Na2S alone. Additionally, the arsenic concen-tration of the tails and the arsenic removal efficiency wereapproximately 176mg/kg lower and around 3.05% greater,respectively, in the presence of both Na2S and CuSO4 thanin the case of 200 g/ton CuSO4 alone at pH 9. The resultsclearly exhibited the strong coupled effect of Na2S andCuSO4 (i.e., the sulphidization of arsenic oxides such as

AS2O3, AS4O6 and AS2O5 and the activation of sulphidizedminerals) and the reinforcement effect of this coupling actionon arsenic flotation with PAX. In order to further examinethe effect of solution pH on arsenic removal via flotation,additional experiments were carried out at a low pH condition(pH 4), and the results are also presented in Fig. 6. Thearsenic concentration of the tails and the arsenic removalefficiency were about 1753mg/kg and 86.54% at pH 4,respectively. Compared with the results at pH 9, the arsenicconcentration of the tails was approximately 1179mg/kglower and the arsenic removal efficiency was around 6.43%higher. The decreased removal efficiency at higher pH wasattributed to the relatively higher oxidation of FeAsS athigher pH, resulting in the greater formation of an oxidationproduct on the surface of FeAsS.45,46) Accordingly, thechemisorption of xanthate onto FeAsS was reduced, whichdecreased the hydrophobicity of the FeAsS surface.45,46) Infact, several studies reported similar trends in which FeAsSfloated better at low pH conditions (ca. pH 3­4).31,45,46)

However, the arsenic removal efficiencies obtained fromthe flotation tests using mixed activators did not meet thewarning criteria of arsenic (50mg/kg) for recycling thetailings, regardless of pH. Hence, to meet the warningcriteria, we conducted additional experiments with scaveng-ing tests to maximize the arsenic removal efficiency.3.2.4 Effect of scavenging

Figure 7 shows the arsenic concentration of the tails andthe arsenic removal efficiency obtained during and after twosubsequent scavenging tests. Here, it should be noted thatsimilar optimization tests with the rougher flotation werecarried out to determine the optimal chemical dosages addedfor the scavenging tests, and the results suggested that thearsenic removal efficiency was maximized at the samechemical dosages as observed from the rougher flotation(data not shown). Hence, the scavenging tests were carriedout using the tails obtained after the rougher flotation withmixed activators (200 g/ton Na2S + 200 g/ton CuSO4) atpH 4. The experiments were conducted with 100 g/ton PAXand 250mL/ton AF-65. The results showed that the arsenicconcentrations of middlings 1, middlings 2, concentrates,and tails were about 135830, 95778, 3711 and 44mg/kg,respectively. The cumulative arsenic removal efficiencies of

Fig. 6 Arsenic concentration of the tails and arsenic removal efficiencyafter flotation. The experiments were carried out with mixed activators(Na2S and CuSO4 concentration = 200 g/ton) at pH 4 and 9. PAX andAF-65 concentrations were 100 g/ton and 250mL/ton, respectively.

J. Choi, K. Park, J. Hong, J. Park and H. Kim2294

middlings 1, middlings 2, and concentrates were about 79.28,98.56 and 99.73%, respectively. Hence, the arsenic concen-tration in the tails was reduced to below the warning criteria(50mg/kg) after the two subsequent scavenging processes,which would render the tailings recyclable. The contentsof cadmium, chromium, copper, lead and zinc in the finalproducts were 1.65, 12.62, 10.03, 11.63 and 76.5mg/kg,respectively, which were also below the warning level forrecycling. Additionally, the yield of final products (i.e., theweight ratio of recyclable products and starting materials)was about 84.58%.

4. Conclusions

The Korean government has currently initiated therestoration of all dormant and/or abandoned mines.Hence, flotation experiments were conducted to recycle theSamkwang mine tailings by reducing the arsenic contentbelow the warning criteria (50mg/kg). The followingconclusions were obtained from the study results.

(1) The arsenic removal was greater in the presence ofPAX than in that of SO or SDS due to the difference in theelectrokinetic properties and the interaction type of collectorswith arsenic-bearing minerals.

(2) The type of activator and pulp pH significantly affectedthe arsenic removal efficiency. The arsenic removal wasmaximized in the presence of mixed activators (Na2S +CuSO4) at low pH due to the coupled role of thesulphidization of arsenic oxides (e.g., AS2O3, AS4O6 andAS2O5), the activation of sulphidized minerals, and theformation of dixanthogen.

(3) A successful flotation process consisting of rougherflotation and two subsequent scavenging flotations (Fig. 8)was designed for recycling the Samkwang mine tailings byreducing the arsenic content to 44mg/kg, which is below thewarning criteria of 50mg/kg. Additionally, about 85% ofthe mine tailings (w/w) were recyclable via the proposedprocess.

Acknowledgements

This research was supported by the Mine ReclamationCorporation Research Fund (MIRECO) and the selection of

research-oriented professor of Chonbuk National Universityin 2013.

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Tailings

Rougher flotation

1st scavenging

Na2S : 200 g/ton, CuSO4 : 200 g/tonPAX : 100 g/tonAF-65 : 250 mL/ton

2nd scavenging

tailsNa2S : 200 g/ton, CuSO4 : 200 g/tonPAX : 100 g/tonAF-65 : 250 mL/ton

Na2S : 200 g/ton, CuSO4 : 200 g/tonPAX : 100 g/tonAF-65 : 250 mL/ton

Recyclable products

tails

tails

Fig. 8 Flowsheet of the flotation process optimized for arsenic removalfrom the Samkwang mine tailings.

Fig. 7 Arsenic concentration of the tails and cumulative arsenic removalefficiency for two subsequent scavenging tests. All experiments werecarried out with mixed activators (Na2S and CuSO4 concentra-tion = 200 g/ton). PAX and AF-65 concentrations were 100 g/ton and250mL/ton, respectively, for all cases.

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