2012-on the fundamental aspects of apatite and quartz flotation using a gram positive strain as a bioreagent

1、Minerals Engineering 48 (2013) 6167On the fundamental aspects of apatite and quartz otation using a Grampositive strain as a bioreagentAntonio G. Merma a, Maurcio L. Torem a, Jos J.V. Morn a, Marisa B.M. Monte ba Department of Materials Engineering, Pontical Catholic University of Rio de Janeiro, Ru

2、a Marqus de So Vicente, 225, Gvea, Rio de Janeiro, RJ 22453-900, Brazilb Laboratory for Surface Chemistry, Center for Mineral Technology CETEM, Av. Pedro Calmon, 900, Cidade Universitria, Rio de Janeiro, RJ 21941-908, Brazila r t i c l e i n f oa b s t r a c tArticle history:Available online 3 Decem

3、ber 2012Mineral biootation encompasses the principles and methods used in mineral otation using microor- ganisms as otation reagents. This work deals with the fundamental aspects of apatite and quartz ota- tion using Rhodococcus opacus bacteria as a bioreagent. Each mineral sample was conditioning w

4、ith the bacterial suspension in a rotary shaker under specic conditions as particle size, biomass concentration, pH solution and conditioning time, for all the studies done during the research. The zeta potential results showed a change in zeta potential measurements of the minerals after the bacter

5、ial interaction. This change was more signicant in the zeta potential curves of apatite than those for quartz. The results also suggest that the bacterial adhesion onto the mineral surfaces was predominantly specic. The greatest apatite otability achieved 90% at pH around 5, in the presence of 150 m

6、g L 1 of bacteria after 5 min of otation. On the other hand, quartz achieved a otability of 14% under identical experimental condi- tions. The fundamental otation studies revealed the prospect that R. opacus presents as a biocollector and biofrother and indicate its promising application in phosphat

7、e otation industry.2012 Elsevier Ltd. All rights reserved.Keywords: Biotechnology Biootation Bioreagents Phosphates Apatite Quartz1. Introductionmetabolic products, thus enriching it, with respect to the desired valuable minerals (Natarajan, 2006; Daz-Lpes et al., 2012; Rao and Subramanian, 2007; Ra

8、o et al., 2010). Biootation exploits the differences in surface characteristics of solids suspended in an aqueous medium, adjusting and controlling their surface ener- giesPhosphate rocksare vitalnonrenewable resources and areessential components in agricultural fertilizers and phosphorous- based ch

9、emicals. In Brazil, about 85% of the phosphate produced is consumed in the fertilizer industry. Phosphate deposits can be divided into three groups: sedimentary, igneous and biogenetic deposits (Alburquerque, 2010).In recent years, mining industry has been facing several prob- lems that inuence the

10、mineral processing, such as the depletion of high-grade ore (Dwyer et al., 2012) and environmental regula- tions (Daz-Lpes et al., 2012). The former aspect compels the min- ing industry to process low grade ores, ne mineral particles and otation tailings to produce material suitable for a global mar

11、ket (Dwyer et al., 2012). Thus, it has become very important to develop appropriate and environmentally friendly technologies able to complement the conventional techniques used at the mineral con- centration. In this context, biobeneciation is increasing its role in mineral processing. The main pur

12、pose of this procedure is to selec- tivity undertake the removal of undesirable mineral constituents from an ore, through interaction with microorganisms and/or theirand interfacial tensions (Pecina et al., 2009) through the useofmicroorganisms with hydrophobic properties (Natarajan, 2006; Pecina et

13、 al., 2009). Biootation is becoming very attractive forpresenting a great technological potential, environmental acceptability, exibility in the choice of microorganisms and espe- cially due to its mineral selectivity (Rao and Subramanian, 2007; Dwyer et al., 2012) and also for processing ne and ult

14、ra-ne min- eral particles (Kuyumcu et al., 2009).One of the most important steps in mineral biootation is the adhesion of the microorganism onto the mineral surface (Jia etal., 2011; Dwyer et al., 2012). The bacterial adhesion occurs asanet result of attractive and repulsive forces of the cell and m

15、ineralsurfaces. The interactions that result in such adhesion include elec- trostatic interactions, acidbase interactions, van der Waals forces and hydrophobic interactions, all of which are determined by the cell-wall and mineral surface properties (Dwyer et al., 2012; Daz- Lpes et al., 2012; Rao a

16、nd Subramanian, 2007). A selective bacterial attachment is desired, onto a specic mineral, in order to modify its surface properties, consequently obtaining the sepa- ration of the desirable mineral (Chun-yun et al., 2008). This surface modication can be direct or indirect; the direct mechanism in-

17、Corresponding author. Tel.: +55 21 3527 1723; fax: +55 21 3527 1236.E-mail addresses: (A.G. Merma), torempuc-rio.br (M.L. Torem), (J.J.V. Morn), .br (M.B.M. Monte).0892-6875/$ - see front matter 2012 Elsevier Ltd. All rights reserved. http:/dx.doi

18、.org/10.1016/j.mineng.2012.10.018Contents lists available at SciVerse ScienceDirectMinerals Engineeringjournal homepage: /locate/mineng62A.G. Merma et al. / Minerals Engineering 48 (2013) 6167volves the adhesion of the bacterial cells to mineral particles, while the indirect mechanis

19、m refers to metabolic products which act like surface activator reagents. Both interactions may allow the mineral surface to acquire hydrophobic or hydrophilic properties (Natarajan, 2006; Rao and Subramanian, 2007; Somasundaran et al., 2000).The literature review shows that the use of bioreagents i

20、n min- eral processing is still in the early stages. In order to have a better understanding of the fundamental aspects of mineral biootation, it is required to signicantly increase the research related to the electrophoretic behavior of minerals/bacteria systems, thermody- namic adhesion of differe

21、nt bioreagents onto mineral surface and biootation kinetics to name a few.The Brazilian igneous phosphate deposits are associated with several gangue minerals, particularly quartz, magnetite, carbon- ates and silicates (Oliveira, 2005). The application of Rhodococcus opacus bacteria in the igneous p

22、hosphate processing will depend on the otation behavior of each mineral present in presence of this bioreagent. The aim of this work was the study of the funda- mental aspects of the biootation of apatite and quartz using a R. opacus strain as a bioreagent, due to its frothing and collecting behavio

23、r. This study considered the inuence of initial pH of the aqueous suspension and bacteria concentration on the electropho- retic behavior, contact angle, surface tension and otability of the minerals before and after interaction with R. opacus bacteria.cally using this medium in Petri plates and sav

24、ing them in a refrigerator at 20 C. Then, the bacteria was sub-cultured in a liquid medium (10.0 g L 1 glucose, 5.0 g L 1 peptone, 3.0 g L 1 malt ex- tract and 3.0 g L 1 yeast extract) at pH 7.2, on a rotary shaker, maintained at 175 rpm and 28 C, during 72 h. Time needed for the bacterialcells to r

25、each the beginning of the stationary phaseof theirgrowth. After that, the bacterial suspension was centri- fuged and the obtained biomass was twice washed with deionized water, thenthe cells were re-suspended in a 10 3 M NaCl solution. Finally, the bacterial concentrate was inactivated in the autocl

26、ave to avoid further bacterial development. Concentration of the cellu- lar suspension was quantied by optical density in a spectropho- tometer (UV-1800, Shimatzu UV-spectrophotometer) at a wavelength of 620 nm.2.3. Zeta potential studiesZeta potential measurements for R. opacus cells, apatite and q

27、uartz were carried out on the micro-electrophoresis apparatus zeta-meter 4.0 + (Zeta-Meter, Inc., Staunton USA). The concentra- tion of the mineral and biomass suspension were both of 100 mg L 1 and NaCl 10 3 M was used as an indifferent electrolyte, pH was adjusted using diluted HCl and NaOH soluti

28、ons. The eval- uation of the zeta potential proles for the minerals was carried out before and after interaction with R. opacus bacteria suspension.2.4. Contact angle and surface tension measurements2. Materials and methodsThe contact angle measurements were carried out through a Goniometer RamHart

29、using the captive bubble method. A min- eral crystal was carefully cut (dimensions at Table 1), and then the surface sample was cautiously polished with a diamond paste containing particles of 3 lm and 1 lm. To remove any particles sticking to the polished surface, the samples were cleaned with jets

30、 of distilled water and ultrasonic water bath. The angle contact measurements of the mineral were taken before and after interac- tion with the bacterial suspension at different pH values. The min- eral section was suspended in a bacterial suspension with0.15 g L 1 of the biomass for 5 min. After th

31、is time, the samples were washed with 10 3 M NaCl solution to remove the bacterial cells that were no stuck. The samples were vacuum dried in a des- iccator for approximately 10 min. Finally, the contact angle mea- surements were carried out. The pH of the solution was adjusted for the same values o

32、f the bacterial suspension previously used, using diluted HCl and NaOH solutions.The surface tension measurements were performed using the ring method in a Kruss K10 digital tensiometer with an accuracy of 0.1 mN m 1. The surface tension of the bacterial suspensions was set at different bacterial co

33、ncentrations and in function of the pH suspension, the pH suspensions were regulated with di- luted HCl and NaOH solutions.2.1. Sample minerals preparationPure apatite and quartz mineral samples were used in this study. Pure apatite sample was provided by the Centre for Mineral Technology (CETEM) an

34、d pure quartz sample was provided by a lo- cal supplier (Estrada Mining, Belo Horizonte, Minas Gerais State). The samples were jaw crushed and dry screened to 3 mm. These samples were then dry-ground in a porcelain mortar and wet screened for obtaining the desired size fractions (Table 1). The groun

35、d quartz was then washed several times in KOH (0.1 M) until a clear supernatant was observed. This quartz material then was repeatedly washed with double-distilled water until the pH of the mineral suspension was the same that at the beginning. After this cleaning procedure the quartz powder was dri

36、ed in air at room temperature. Then all samples were stored in a desiccator.2.2. Microorganisms, media and growthR. opacus strain was supplied by the Brazilian Collection of Envi- ronmental and Industrial Microorganisms (CBMAI-UNICAMP). It is a non-pathogenic, Gram-positive and chemoorganotrophic or

37、gan- ism, which presents a high hydrophobicity (contact angle around 70 ) (Mesquita et al., 2003). It was cultivated in a maintenance so- lid medium (10.0 g L 1 glucose, 5.0 g L 1 peptone, 3.0 g L 1 malt extract and 3.0 g L 1 yeast extract, 2.0 g L 1 CaCO3, and 12 g L 1 agar). Stocks of the bacteria

38、 were prepared and renewed periodi-2.5. Microotation experimentsThe microotation evaluation was carried out in a modiedHallimond tube. An amount of 1.0 g of mineral was added to0.16 L total volume suspension of known bacterial concentration; the pH was adjusted with diluted HCl and NaOH solutions. T

39、he mineral was conditioned with the bacterial suspension inside the Hallimond tube under constant stirring for about 5 min, and then the mineral otation tests were carried out using air at a ow rate of 15 ml/min during 7 min. The settled and oated fractions were carefully separated, washed, dried an

40、d weighed. The otability was then calculated as the ratio of oated and non-oated mineral amounts and the total weighed sample.Table 1Particle size (d80) for the experimental work.Experimental workParticle size (lm)20 lm(150105) lm(10575) lm(7538) lmZeta potentialMicrootation experiments Contact angl

41、e measurements(0.5 0.5 1.0) cmA.G. Merma et al. / Minerals Engineering 48 (2013) 616763The zeta potential prole of apatite and quartz can also be seen at Fig. 1. A negative surface charge was observed for both minerals over the studied pH range; in addition, it was not possible to estab- lish the IE

42、P value for both minerals. However, IEP values of apatite between 2.0 and 8.0 were reported (Barros et al., 2008; Hu and Xu, 2003; Kou et al., 2010). This apatite behavior could be explained due to its tolerance to isomorphic substitutions, regardless of its origin and composition, factors which alt

43、er the IEP value of the mineral. Nevertheless, the IEP values of quartz, reported in litera- ture, are more stable and normally around between pH 1.8 and 3.0 (Lopes, 2009; Turrer, 2007; Viana, 2006; Vieira, 2005;Rodrigues, 2007).Fig. 1 also presents the zeta potential curves of apatite and quartz af

44、ter interaction with R. opacus. A variation was observed in the surface properties of apatite after interaction with the bacte- ria cells in all the pH range studied. Moreover, this change was more signicant at pH 5, where the zeta potential value of the min- eral after bacterial interaction seems t

45、o be similar to that of the bacteria cells. Below this pH value it is more difcult to see this ef- fect, since the zeta potential values of the mineral samples before and after the bacterial interaction were very similar. Furthermore, the zeta potential curves of quartz were also affected by the pre

46、s- ence of the bacteria cells, but the change was less signicant than in the case of apatite. However, the same behavior was presented in pH range 5, where the zeta potential values of quartz were sim- ilar to zeta potential values of bacteria cells.The observed shift in potential zeta values of bot

47、h minerals, after the interaction with R. opacus cells, could be related to the adsorption of the cells and/or metabolic products onto the mineral surface (Somasundaran et al., 2005; Vilinska and Rao, 2008; Dubel et al., 1992; Raichur et al., 1996; Faharat et al., 2008; Botero et al., 2008; Mesquita

48、 et al., 2003; Deo et al., 2001; Subramanian et al., 2003; Chandraprabha and Natarajan, 2006).2.6. SEM micrographic analysisThe bacterial suspension sample was centrifuged at 3000 rpm, and then chemically xed for a period of 2448 h at 40 C using glutaraldehyde. After that, the sample was rinsed in d

49、istilled water to remove traces of glutaraldehyde; and nally the samples were dehydrated in graded series of ethanol or acetone, and air dried under vacuum. The samples were coated with a lm of gold using a vacuum coating device and loaded for SEM studies in a FEI Quanta 400 microscopy. The mineral

50、samples were prepared with the same procedure used to prepare bacterial sample. The detailed experimental procedure is described elsewhere (Merma, 2012).3. Results and discussion3.1. Zeta potential studiesThis study deals with the changes in electrophoretic patterns of mineral samples after interact

51、ions with R. opacus bacterial at dif- ferent pH values. Any changes in the surface charge of the mineral were related to adhesion of bacteria cells, these changes could also help to elucidate the interaction mechanisms between the cells and the active site of the mineral surface.Fig. 1 shows the zet

52、a potential curves of R. opacus cells and min- eral particles at different pH values. The surface of the R. opacus cells is negatively charged over a wide range of pH, presenting an IEP (isoelectric point) value around 2.8. This result is in good accordance with those obtained by Mesquita et al. (20

53、03) and Botero et al. (2008), an IEP around 3.2. The difference found may be related to different reasons as the grown conditions and also the source of the strain. The acidic IEP value of R. opacus could be associated to the presence of anionic groups on the bacterial wall- cell that dominate over

54、the cationic groups. The presence of these anionic and cationic groups gives amphoteric properties to the bacterial wall, which implies that the net charge is strongly pH dependent (Rao and Subramanian, 2007; Natarajan, 2006; Vilinska and Rao, 2008; Faharat et al., 2008; Van Der Wal et al., 1997). F

55、urthermore, it was observed, at the pH range between 2 and 5, a3.2. Surface tension of R. opacus suspensionFig. 2 displays the surface tension of bacterial suspensions at airwater interface at 23 C and pH 5. It was observed that when the biomass concentration was increased, the surface tension of th

56、e suspension was decreased. In this way, with 0.05 g L 1 of the biomass, the surface tension showed a small decrease in compari- son with that of pure water ( 70 mN/m). When the concentration of the biomass was 0.1 g L 1, then, the surface tension decreased signicantly, but beyond this concentration

57、 the surface tensionformation of large agglomerates of bacterial cells whichisprobably due to the reduction of electrostatic repulsion around its IEP value.R. opacusQuartz before contact Quartz after contact Apatite before contact1072 Apatite after contact 068-1064-2060-3056-4052-5048246810120.40.00

58、.pHBacterial concentration (g/L)Fig. 1. Zeta potential of quartz and apatite samples before and after R.opacusFig. 2. Surface tension of R. opacus suspensions at different concentrations of the biomass, pH 5.5.interaction. NaCl 10 3 M as background electrolyte. Bacterial concentration,0.10 g L 1.Zeta Potential (mV