Adhesion of Escherichia coli onto quartz, hematite and corundum: Extended DLVO theory and flotation behavior

doi:10.1016/j.colsurfb.2009.07.009

Colloids and Surfaces B: Biointerfaces

Volume 74, Issue 1, 1 November 2009, Pages 140-149

https://doi.org/10.1016/j.colsurfb.2009.07.009 Get rights and content

Abstract

The adhesion of Escherichia coli onto quartz, hematite and corundum was experimentally investigated. A strain of E. coli was used that had the genes for expressing protein for silica precipitation. The maximum cell adhesion was observed at pH <4.3 for quartz and at pH 4.5–8.5 for corundum. For hematite, cell adhesion remained low at all pH values. The microbe–mineral adhesion was assessed by the extended DLVO theory approach. The essential parameters for calculation of microbe–mineral interaction energy (Hamaker constants and acid–base components) were experimentally determined. The extended DLVO approach could be used to explain the results of the adhesion experiments. The effect of E. coli on the floatability of three oxide minerals was determined and the results showed that E. coli can act as a selective collector for quartz at acidic pH values, with 90% of the quartz floated at 1.5 × 10⁹ cells/ml. However, only 9% hematite and 30% corundum could be floated under similar conditions. By using E. coli and no reagents, it was possible to separate quartz from a hematite–quartz mixture with Newton's efficiency of 0.70. Removal of quartz from the corundum mixture was achieved by E. coli with Newton's efficiency of 0.62.

Introduction

Utilization of microorganisms as bioreagents in mineral processing (bioflotation or bioflocculation) gave hopes for upgrading minerals from ores by economical and environmentally safe processes. The separation of minerals by biobeneficiation is governed by selective adhesion of microbial cells onto mineral surfaces and the changes occurred on mineral surfaces after the biotreatment. The adhesion of microbial cells onto mineral surfaces is influenced by several properties such as the surface charge, surface free energy components, and the presence and configuration of surface polymers. In general, bacterial adhesion can be explained by surface thermodynamics and the extended DLVO theory, in which the adhesion energy between cells and substrate is calculated as a function of the separation distance [1], [2], [3]. These methods take into account Lifshitz–van der Waals interactions, electrostatic interactions, and hydrophobic/hydrophilic force (acid–base) interactions. The most important input in these calculations is the surface energy and its different components (surface charge, Hamaker constants, electron donating, and electron accepting) on the bacterial cell surface and solid substrate. The microbial adherence on mineral surface and the subsequence formation of biofilm result in changes in surface properties which can be exploited in mineral separation. For example, hematite surface gained hydrophobic properties after being treated with Mycobacterium phlei cells [4], [5]. However, hematite gained hydrophilic properties after interaction with Bacillus polymyxa. B. plymyxa rendered quartz hydrophobic properties after sorption on its surface [6]. Escherichia coli was found to be act as a flotation collector for quartz under acidic conditions [7]. In this case, the E. coli strain was genetically modified to express silica-inducing protein (sip), believed to facilitate adhesion and modify mineral surface properties.

The sip modified strain of E. coli was derived from a mutation of the E. coli JM109 strain that has sip cloned in the pET32 vector. The sip genes were cloned from the hyperthermophilic bacteria Thermus thermophilus [8].

Hematite and corundum are important industrial minerals; hematite is the principle source of iron. Huge amounts are mined annually for industrial production. Corundum is used as an abrasive in the manufacture of sandpaper, polishing components and cutting tools. The presence of silica in association with hematite and corundum as gangue mineral, affects on their commercial uses. From this point of view, this study investigates the adhesion behavior of E. coli strain sip onto the three oxide minerals experimentally and theoretically by extended DLVO theory. Surface energy components of the microbe and the mineral samples (Hamaker constants and acid–base components) were experimentally determined from contact angle measurements. Subsequent changes on the mineral surface after biotreatment were followed by measuring the mineral zeta potential and contact angles. Flotation behavior and possibility to remove silica from hematite/corundum mixture were investigated through single mineral and differential microflotation experiments.

Section snippets

Mineral samples

Hand-picked natural pure samples of quartz, hematite, and corundum were obtained from different locations. Quartz was obtained from Ishikawa Prefecture, Japan, while the hematite sample was obtained from the Bahariya Oasis, Egypt. The ruby corundum sample was from Southern District, Madagascar. The samples were crushed with a hammer and ground in a planetary ball mill (Fritch pulverisette 6). The ground samples were sieved to obtain the −105 μm + 78 μm size fraction for flotation experiments and

Estimation of interaction energies by extended DLVO theory

The interaction energy between the microbe and quartz, corundum, and hematite was calculated using the extended DLVO theory. The classical DLVO theory as described by Verwey and Overbeek [11] and Deryagin and Landau [12] includes attractive or repulsive electrostatic forces and Lifshitz–van der Waals attractive forces (LW). The acid–base interaction component, which is based on electron donating and electron accepting interactions between polar moieties in aqueous solution, was added by van Oss

Conclusions

The results of the adhesion experiment show that E. coli strain sip has higher affinity to quartz than to hematite or corundum, especially at pH <4.3. However, in the alkaline region, the number of cells adsorbed onto quartz and other minerals decreases. The calculated energy components of mineral samples and cells show that the microbial cells have hydrophobic properties, while the minerals are hydrophilic. The effect of pH on the total interaction energy of the mineral–microbial cells

Acknowledgments

Financial support was provided by the Japan Society for the Promotion of Science (JSPS), the New Energy and Industrial Technology Development Organization (NEDO), and the Ministry of Higher Education and Scientific Research, Egypt.

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Adhesion of Escherichia coli onto quartz, hematite and corundum: Extended DLVO theory and flotation behavior

Abstract

Introduction

Section snippets

Mineral samples

Estimation of interaction energies by extended DLVO theory

Conclusions

Acknowledgments

Adv. Colloid Interface Sci.

Miner. Eng.

Int. J. Miner. Process.

Miner. Eng.

Miner. Eng.

J. Colloid Interface Sci.

Licentiate thesis

Physico-chemical characterization of microbial cell surface and bioflotation of sulfide minerals

FEMS Microbiol. Rev.

Appl. Environ. Microbiol.