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The flotation of apatite and quartz was investigated using R. opacus bacteria as a bioreagent. Microflotation tests in a modified Hallimond tube were used to study the effects of the initial pH of the aqueous suspension and bacteria concentration on the electrophoretic behaviour, contact angle, surface tension and flotability of the minerals before and after interaction with R. opacus bacteria. The biomass modified the zeta potential profiles of apatite and quartz, with the change being more significant in the case of apatite. The surface tension of the bacterial suspension was dependent on the solution pH and the bacterial concentration. A lower surface tension value was observed in the presence of 0.15 g/l of biomass and pH values in the range 3-7. The bioflotation of apatite and quartz particles was also found to be dependent on the pH and the bacterial concentration. Higher flotability of both minerals was observed at pH around 5 using 0.15 g/l of biomass and an air flow rate of 15 ml/min. After 5 minutes of flotation values of about 90% and 14% were obtained for apatite and quartz, respectively. Scanning electron microscopy images showed the presence of R. opacus cells attached to both mineral surfaces, but more bacterial cells adhered to the apatite surface. The results indicate a higher affinity of R. opacus cells for the apatite surface and suggest that the bacteria may be a promising biocollector and biofrother in phosphate flotation., The flotation of apatite and quartz was investigated using R. opacus bacteria as a bioreagent. Microflotation tests in a modified Hallimond tube were used to study the effects of the initial pH of the aqueous suspension and bacteria concentration on the electrophoretic behaviour, contact angle, surface tension and flotability of the minerals before and after interaction with R. opacus bacteria. The biomass modified the zeta potential profiles of apatite and quartz, with the change being more significant in the case of apatite. The surface tension of the bacterial suspension was dependent on the solution pH and the bacterial concentration. A lower surface tension value was observed in the presence of 0.15 g/l of biomass and pH values in the range 3-7. The bioflotation of apatite and quartz particles was also found to be dependent on the pH and the bacterial concentration. Higher flotability of both minerals was observed at pH around 5 using 0.15 g/l of biomass and an air flow rate of 15 ml/min. After 5 minutes of flotation values of about 90% and 14% were obtained for apatite and quartz, respectively. Scanning electron microscopy images showed the presence of R. opacus cells attached to both mineral surfaces, but more bacterial cells adhered to the apatite surface. The results indicate a higher affinity of R. opacus cells for the apatite surface and suggest that the bacteria may be a promising biocollector and biofrother in phosphate flotation.

Mining and metallurgical waste waters are considered to be major sources of heavy metal contamination. The heavy metals are conventionally recovered by precipitation, ion exchange or activated carbon sorption, but these methods are characterised by low recovery efficiencies and high costs. The advantages of biosorption include good performance in metals removal and cost-effectiveness as they make use of raw materials from fermentation and agricultural processes. The ability of Streptomyces lunalinharesii to sorb Cu and Zn from aqueous solutions was investigated using batch experiments at 25 degrees C. The effects of sorption parameters such as contact time, initial metal concentration, pH and biomass concentration on the sorption capacity were studied. The biosorbent was effective in removing Cu and Zn, with equilibrium achieved in 30 minutes at pH 6.0 and 5.0, respectively, for Zn and Cu. The equilibrium sorption figures were fitted to Langmuir and Freundlich adsorption isotherm models and the model parameters evaluated. The pseudo-second-order rate equation provided a better description of the biosorption process. FT-IR analysis showed that hydroxyl, carboxyl and amine groups were the major binding groups., Mining and metallurgical waste waters are considered to be major sources of heavy metal contamination. The heavy metals are conventionally recovered by precipitation, ion exchange or activated carbon sorption, but these methods are characterised by low recovery efficiencies and high costs. The advantages of biosorption include good performance in metals removal and cost-effectiveness as they make use of raw materials from fermentation and agricultural processes. The ability of Streptomyces lunalinharesii to sorb Cu and Zn from aqueous solutions was investigated using batch experiments at 25 degrees C. The effects of sorption parameters such as contact time, initial metal concentration, pH and biomass concentration on the sorption capacity were studied. The biosorbent was effective in removing Cu and Zn, with equilibrium achieved in 30 minutes at pH 6.0 and 5.0, respectively, for Zn and Cu. The equilibrium sorption figures were fitted to Langmuir and Freundlich adsorption isotherm models and the model parameters evaluated. The pseudo-second-order rate equation provided a better description of the biosorption process. FT-IR analysis showed that hydroxyl, carboxyl and amine groups were the major binding groups.

The affinity was studied of Rhodococcus opacus cells for calcite and magnesite surfaces to evaluate its application as a flotation collector. The mineral infra-red spectra before and after bacterial interaction indicated that a mineral surface interaction occurred with the R. opacus cell wall. Zeta potential curves obtained before and after interaction showed that the microorganism modified the reversal charge of calcite and magnesite. Thermodynamic analysis showed that the total free energy value of the adhesion of R. opacus on magnesite is more negative than for calcite, indicating greater affinity for the magnesite surface., The affinity was studied of Rhodococcus opacus cells for calcite and magnesite surfaces to evaluate its application as a flotation collector. The mineral infra-red spectra before and after bacterial interaction indicated that a mineral surface interaction occurred with the R. opacus cell wall. Zeta potential curves obtained before and after interaction showed that the microorganism modified the reversal charge of calcite and magnesite. Thermodynamic analysis showed that the total free energy value of the adhesion of R. opacus on magnesite is more negative than for calcite, indicating greater affinity for the magnesite surface.

Electroflotation is a simple process which involves the flotation of pollutants to the surface by tiny bubbles of hydrogen and oxygen generated by the electrolysis of water. Advantages include the cleanliness of the water obtained after treatment, and disadvantages are low productivity, high maintenance and electrode costs and the large volume of sludge produced. In the electrocoagulation process, the coagulant is generated in situ by electrolytic oxidation of an appropriate anode material such as Fe or Al. Charged ionic species are removed from the wastewater by allowing it to react with ions having opposite charge or with a floc of metallic hydroxides generated within the effluent. Metal ions are generated at the anode and hydrogen gas is released from the cathode. The performance of an electroflotation system is affected by the pH and temperature of the wastewater. Current density is critical for electrocoagulation since it is the only operational parameter that can be directly controlled. Advantages of the method include high particulate removal efficiency, compact treatment facility, relatively low cost and possibility of complete automation, and disadvantages are the need for periodical replacement of electrodes, electricity costs and the requirement for high conductivities of the wastewaters., Electroflotation is a simple process which involves the flotation of pollutants to the surface by tiny bubbles of hydrogen and oxygen generated by the electrolysis of water. Advantages include the cleanliness of the water obtained after treatment, and disadvantages are low productivity, high maintenance and electrode costs and the large volume of sludge produced. In the electrocoagulation process, the coagulant is generated in situ by electrolytic oxidation of an appropriate anode material such as Fe or Al. Charged ionic species are removed from the wastewater by allowing it to react with ions having opposite charge or with a floc of metallic hydroxides generated within the effluent. Metal ions are generated at the anode and hydrogen gas is released from the cathode. The performance of an electroflotation system is affected by the pH and temperature of the wastewater. Current density is critical for electrocoagulation since it is the only operational parameter that can be directly controlled. Advantages of the method include high particulate removal efficiency, compact treatment facility, relatively low cost and possibility of complete automation, and disadvantages are the need for periodical replacement of electrodes, electricity costs and the requirement for high conductivities of the wastewaters.

The use is discussed of kaolin pulps as coatings in the paper industry. Laminar movement of concentrated pulps is difficult without the use of dispersing agents. The zeta potential and rheology were investigated of kaolin samples with and without the use of sodium hexametaphosphate as dispersant. Total interparticle interaction energy was calculated using DLVO theory. The results showed that the anions generated are chemically adsorbed by the kaolin preferentially to the edges faces. Increasing the pH and dispersant addition resulted in an increasingly negative zeta potential and a liquefying effect on the concentrated pulps. Qualitative agreement was obtained between DLVO theory and the rheological behaviour of the pulps., The use is discussed of kaolin pulps as coatings in the paper industry. Laminar movement of concentrated pulps is difficult without the use of dispersing agents. The zeta potential and rheology were investigated of kaolin samples with and without the use of sodium hexametaphosphate as dispersant. Total interparticle interaction energy was calculated using DLVO theory. The results showed that the anions generated are chemically adsorbed by the kaolin preferentially to the edges faces. Increasing the pH and dispersant addition resulted in an increasingly negative zeta potential and a liquefying effect on the concentrated pulps. Qualitative agreement was obtained between DLVO theory and the rheological behaviour of the pulps.

An investigation was carried out into the use of foam separation techniques such as ionic flotation, precipitate flotation and adsorbing colloid flotation for recovering and removing metal ions from dilute solutions. The fundamental characteristics of the methods and their potential for industrial application were studied for the removal of Cd(II), Cr(III) and As(V). The effects of pH, collector and frother concentration, gas flow-rate and chemical speciation were considered in relation to the surface chemistry processes involved. The results showed that 98.8% Cd(II) removal can be achieved by ionic flotation using a metal:collector (sodium dodecylsulphate) ratio of 1:2, 0.1vol% isopropanol, gas flow rate of 2 ml/s and pH 4-5. Cr(III) can be successfully removed and 96.2% recovered by precipitate flotation using a sodium dodecylsulphate concentration of 1 x 10-4 mol/l, 0.1vol% ethanol, gas flow rate of 2.1 ml/s and pH 8. Removal of 99.9% of As(V) can be obtained by adsorbing colloid flotation using a sodium dodecylsulphate concentration of 100 mg/l, Fe(III) concentration of 160 mg/l, gas flow rate of 2.0 ml/s and pH 5-6., An investigation was carried out into the use of foam separation techniques such as ionic flotation, precipitate flotation and adsorbing colloid flotation for recovering and removing metal ions from dilute solutions. The fundamental characteristics of the methods and their potential for industrial application were studied for the removal of Cd(II), Cr(III) and As(V). The effects of pH, collector and frother concentration, gas flow-rate and chemical speciation were considered in relation to the surface chemistry processes involved. The results showed that 98.8% Cd(II) removal can be achieved by ionic flotation using a metal:collector (sodium dodecylsulphate) ratio of 1:2, 0.1vol% isopropanol, gas flow rate of 2 ml/s and pH 4-5. Cr(III) can be successfully removed and 96.2% recovered by precipitate flotation using a sodium dodecylsulphate concentration of 1 x 10-4 mol/l, 0.1vol% ethanol, gas flow rate of 2.1 ml/s and pH 8. Removal of 99.9% of As(V) can be obtained by adsorbing colloid flotation using a sodium dodecylsulphate concentration of 100 mg/l, Fe(III) concentration of 160 mg/l, gas flow rate of 2.0 ml/s and pH 5-6.

Studies were carried out of very dilute solutions using cetyl trimethyl ammonium bromide (CTAB) as a collector. The ultimate recovery, upgrade ratio and volume reduction were studied as a function of air flow rate, bubble size and froth depth. Results showed that, for pH around 11, a surfactant level around 0.030 g/dm3 of CTAB was needed to achieve a gold recovery of 90%. Gold recovery was found to be directly dependent on air flowrate, but volume reduction and upgrade ratio were inversely dependent on this. The froth depth barely affected recovery, and increasing froth depth raised the upgrade ratio and volume reduction. All three factors studied increased as the bubble size decreased., Studies were carried out of very dilute solutions using cetyl trimethyl ammonium bromide (CTAB) as a collector. The ultimate recovery, upgrade ratio and volume reduction were studied as a function of air flow rate, bubble size and froth depth. Results showed that, for pH around 11, a surfactant level around 0.030 g/dm3 of CTAB was needed to achieve a gold recovery of 90%. Gold recovery was found to be directly dependent on air flowrate, but volume reduction and upgrade ratio were inversely dependent on this. The froth depth barely affected recovery, and increasing froth depth raised the upgrade ratio and volume reduction. All three factors studied increased as the bubble size decreased.

Detailed mineralogical characterisation was carried out using scanning electron microscope, energy dispersive spectrometer and X-ray diffraction techniques. Superficial treatments with HCl, HNO3 and HF were also carried out to evaluate the modifications on surface compositions and the morphology of the particles for flotation purposes. The studies showed that both xenotime and zircon present very small inclusions of thorite, zircon is strongly metamicitised giving rise to malacon. The HF pretreatment deeply affected the morphology of the particles as well as the surface properties in relation to flotation., Detailed mineralogical characterisation was carried out using scanning electron microscope, energy dispersive spectrometer and X-ray diffraction techniques. Superficial treatments with HCl, HNO3 and HF were also carried out to evaluate the modifications on surface compositions and the morphology of the particles for flotation purposes. The studies showed that both xenotime and zircon present very small inclusions of thorite, zircon is strongly metamicitised giving rise to malacon. The HF pretreatment deeply affected the morphology of the particles as well as the surface properties in relation to flotation.

The pilot plant at Taboca Mining's Pitinga cassiterite mine in Brazil produces significant amounts of zircon and xenotime in its middlings. Flotation of these is investigated, using anionic (oleic acid and a linoleic/oleic acid mixture) and cationic (amine acetate) collectors, with and without pretreatment by superficial leaching with cold nitric or hydrochloric acid. Both minerals are optimally liberated in the 106 to 212 micron size fraction. Zeta potential tests indicate that the isoelectric points for xenotime and zircon correspond to pH 4.5 and 4.7 respectively; pretreatment displaced these to a lower pH value. Microflotation tests indicate that the floatabilities of both pretreated and untreated minerals are similar for the collectors studied. There is little selectivity between the minerals for the conditions examined. Mechanisms for the adsorption are suggested., The pilot plant at Taboca Mining's Pitinga cassiterite mine in Brazil produces significant amounts of zircon and xenotime in its middlings. Flotation of these is investigated, using anionic (oleic acid and a linoleic/oleic acid mixture) and cationic (amine acetate) collectors, with and without pretreatment by superficial leaching with cold nitric or hydrochloric acid. Both minerals are optimally liberated in the 106 to 212 micron size fraction. Zeta potential tests indicate that the isoelectric points for xenotime and zircon correspond to pH 4.5 and 4.7 respectively; pretreatment displaced these to a lower pH value. Microflotation tests indicate that the floatabilities of both pretreated and untreated minerals are similar for the collectors studied. There is little selectivity between the minerals for the conditions examined. Mechanisms for the adsorption are suggested.

The electrophoretic behaviour was studied of calcite and magnesite before and after treatment with R. opacus. Adsorption of the R. opacus cells shifted the zeta-potential curves and the reversal charges of the two minerals compared with their original isoelectric points. Adhesion tests suggested a higher affinity of the bacteria for magnesite than calcite. The adsorption rates on calcite and magnesite exhibited rapid kinetics, maximum cell adsorption being achieved after 5 min. Adsorption isotherm curves exhibited Langmurian type II behaviour. Optimum recoveries for magnesite and calcite were about 93% using a R. opacus concentration of 100 ppm at pH around 5.0 and 55% using a R. opacus concentration of 220 ppm at pH around 7.0, respectively., The electrophoretic behaviour was studied of calcite and magnesite before and after treatment with R. opacus. Adsorption of the R. opacus cells shifted the zeta-potential curves and the reversal charges of the two minerals compared with their original isoelectric points. Adhesion tests suggested a higher affinity of the bacteria for magnesite than calcite. The adsorption rates on calcite and magnesite exhibited rapid kinetics, maximum cell adsorption being achieved after 5 min. Adsorption isotherm curves exhibited Langmurian type II behaviour. Optimum recoveries for magnesite and calcite were about 93% using a R. opacus concentration of 100 ppm at pH around 5.0 and 55% using a R. opacus concentration of 220 ppm at pH around 7.0, respectively.

The flotation of Au was investigated from very dilute solutions using the surfactant cetyl trimethyl ammonium bromide (CTAB) as collector in Hallimond tube experiments. The results showed that at a pH of about 11 a CTAB dosage of about 0.030 g/dm3, equivalent to 3.5 times the collector/metal stoichiometric ratio, was required to achieve an Au recovery of 90%. The upgrade ratio and volume reduction were affected by the bubble size swarm, gas flow rate and froth depth., The flotation of Au was investigated from very dilute solutions using the surfactant cetyl trimethyl ammonium bromide (CTAB) as collector in Hallimond tube experiments. The results showed that at a pH of about 11 a CTAB dosage of about 0.030 g/dm3, equivalent to 3.5 times the collector/metal stoichiometric ratio, was required to achieve an Au recovery of 90%. The upgrade ratio and volume reduction were affected by the bubble size swarm, gas flow rate and froth depth.

An electroflotation/electrocoagulation cell was used to study the effects of parameters such as collector concentration, potential and current density on the removal of Zn from synthetic solutions containing 20 mg/l Zn. A Pt anode and stainless steel mesh cathode were used in the electroflotation cell. The results showed that it was possible to achieve 96% Zn removal by electroflotation using sodium dodecyl sulphate as collector in the stoichiometric ratio 1:3 at a current density of around 8 mA/cm2 and an inlet pH of about 7.0., An electroflotation/electrocoagulation cell was used to study the effects of parameters such as collector concentration, potential and current density on the removal of Zn from synthetic solutions containing 20 mg/l Zn. A Pt anode and stainless steel mesh cathode were used in the electroflotation cell. The results showed that it was possible to achieve 96% Zn removal by electroflotation using sodium dodecyl sulphate as collector in the stoichiometric ratio 1:3 at a current density of around 8 mA/cm2 and an inlet pH of about 7.0.

The study addressed the production of stabilised yttrium-zirconium oxide powder from zirconium oxychloride and yttrium chloride using urea as a precipitating agent and polyacrylic acid as a dispersing agent. A factorially-designed series of experiments was undertaken to study the effects of some precipitation variables - temperature, time and reagent concentrations - on the aggregate size and electrophoretic mobility and on the crystalline structure of the calcined zirconium oxide powders. It is suggested that the structure of the dispersion species strongly influences the crystal structure of calcined zirconium oxide powders. The role of polyacrylic acid as a dispersing agent is evaluated using DLVO and extended DLVO theory., The study addressed the production of stabilised yttrium-zirconium oxide powder from zirconium oxychloride and yttrium chloride using urea as a precipitating agent and polyacrylic acid as a dispersing agent. A factorially-designed series of experiments was undertaken to study the effects of some precipitation variables - temperature, time and reagent concentrations - on the aggregate size and electrophoretic mobility and on the crystalline structure of the calcined zirconium oxide powders. It is suggested that the structure of the dispersion species strongly influences the crystal structure of calcined zirconium oxide powders. The role of polyacrylic acid as a dispersing agent is evaluated using DLVO and extended DLVO theory.

Ion flotation is a process whereby metal ions are removed from solutions by interaction with a collector that adsorbs preferentially at the solution-air interface. The ions can therefore be removed by bubbling air through the solutions and separating the resulting foam. In the study reported, the removal of cadmium using sodium dodecyl sulphate as a collector and the effects of high ionic strength from NaCl and Na2SO4 were studied. The best removal obtained was about 90% for a collector:metal ratio of 1:2. Ion flotation is very sensitive to the increase in ionic strength which drastically reduces the removal of Cd2+ species., Ion flotation is a process whereby metal ions are removed from solutions by interaction with a collector that adsorbs preferentially at the solution-air interface. The ions can therefore be removed by bubbling air through the solutions and separating the resulting foam. In the study reported, the removal of cadmium using sodium dodecyl sulphate as a collector and the effects of high ionic strength from NaCl and Na2SO4 were studied. The best removal obtained was about 90% for a collector:metal ratio of 1:2. Ion flotation is very sensitive to the increase in ionic strength which drastically reduces the removal of Cd2+ species.

Brazilian kaolin production is increasing, mainly due to the development of new enterprises along the Capim and Jari rivers. These deposits account for 80% of Brazilian resources. Total Brazilian production in 1995 was 1 957 750 t with a production value of US, Brazilian kaolin production is increasing, mainly due to the development of new enterprises along the Capim and Jari rivers. These deposits account for 80% of Brazilian resources. Total Brazilian production in 1995 was 1 957 750 t with a production value of US

The removal of Cd by ion flotation using sodium dodecylsulphate (SDS) as collector was studied. The effects of frothers and ionic strength were also studied, the sublate was characterised by scanning electron microscopy and the surface tension of the initial solutions was measured. In the presence of SDS, the maximum recovery obtained at a stoichiometric metal:collector ratio of 1:3 was 99.1% but a large volume of wet foam was produced. The best recovery (89.2%) with a dry foam was obtained at a ratio of 1:2. The use of frothers gave the highest recovery of Cd at a concentration of 0.1% v/v, where the flotability was 98.8% for iso-propanol and 97.7% for MIBC. An increase in the magnitude of ionic strength significantly decreased Cd removal. A decrease in flotability of Cd was seen as surface tension dropped and the morphology of the sublate and the foam was found to depend on the physico-chemical conditions of the system., The removal of Cd by ion flotation using sodium dodecylsulphate (SDS) as collector was studied. The effects of frothers and ionic strength were also studied, the sublate was characterised by scanning electron microscopy and the surface tension of the initial solutions was measured. In the presence of SDS, the maximum recovery obtained at a stoichiometric metal:collector ratio of 1:3 was 99.1% but a large volume of wet foam was produced. The best recovery (89.2%) with a dry foam was obtained at a ratio of 1:2. The use of frothers gave the highest recovery of Cd at a concentration of 0.1% v/v, where the flotability was 98.8% for iso-propanol and 97.7% for MIBC. An increase in the magnitude of ionic strength significantly decreased Cd removal. A decrease in flotability of Cd was seen as surface tension dropped and the morphology of the sublate and the foam was found to depend on the physico-chemical conditions of the system.

The study explores the ability of Rhodococcus opacus bacteria strain to remove Ni(II) under different experimental conditions using synthetic solutions. The effects of relevant parameters such as solution pH, biomass loading, ionic strength and temperature on Ni(II) biosorption capacity were evaluated. The dynamics of the sorption process were studied and the values of rate constants for different kinetic models were calculated. The activation energy of biosorption was determined as 12.56 kJ/mol., The study explores the ability of Rhodococcus opacus bacteria strain to remove Ni(II) under different experimental conditions using synthetic solutions. The effects of relevant parameters such as solution pH, biomass loading, ionic strength and temperature on Ni(II) biosorption capacity were evaluated. The dynamics of the sorption process were studied and the values of rate constants for different kinetic models were calculated. The activation energy of biosorption was determined as 12.56 kJ/mol.

Mineralogical studies on a low-grade sulphide ore from the Morro do Ouro mine, Minas Gerais, Brazil showed that it contained 65% quartz, 9% pyrite, 7.3% arsenopyrite and minor quantities of other minerals. Most of the Au occurred on the boundaries of or locked in pyrite and arsenopyrite coarse grains. Flotation studies were carried out using potassium amyl xanthate and sodium mercapto benzothiazole as collectors. An increase in collector concentration was required to obtain a higher degree of hydrophobic coverage of the particles and to promote the stability of the particle-bubble aggregates. Optimum results were achieved in the presence of 60 g/t of potassium amyl xanthate, with Au and S recoveries of 85.33 and 56.64%, respectively., Mineralogical studies on a low-grade sulphide ore from the Morro do Ouro mine, Minas Gerais, Brazil showed that it contained 65% quartz, 9% pyrite, 7.3% arsenopyrite and minor quantities of other minerals. Most of the Au occurred on the boundaries of or locked in pyrite and arsenopyrite coarse grains. Flotation studies were carried out using potassium amyl xanthate and sodium mercapto benzothiazole as collectors. An increase in collector concentration was required to obtain a higher degree of hydrophobic coverage of the particles and to promote the stability of the particle-bubble aggregates. Optimum results were achieved in the presence of 60 g/t of potassium amyl xanthate, with Au and S recoveries of 85.33 and 56.64%, respectively.

The correlation is described between the flotation response of coarse particles containing gold and the reagent concentration system for very low-grade auriferous sulphide ore. An increase of collector concentration was needed for a higher degree of hydrophobic coverage of the particles, favouring the stability of the particle-bubble aggregate., The correlation is described between the flotation response of coarse particles containing gold and the reagent concentration system for very low-grade auriferous sulphide ore. An increase of collector concentration was needed for a higher degree of hydrophobic coverage of the particles, favouring the stability of the particle-bubble aggregate.

This paper investigates the potential of precipitate flotation for the removal of chromium from aqueous streams as a technique for wastewater polishing.. A 96.2% maximum removal was achieved at pH around 8.0 and the flotation kinetics of chromium precipitates followed a first order equation., This paper investigates the potential of precipitate flotation for the removal of chromium from aqueous streams as a technique for wastewater polishing.. A 96.2% maximum removal was achieved at pH around 8.0 and the flotation kinetics of chromium precipitates followed a first order equation.

The use of microorganisms and/or their metabolic products is becoming an attractive alternative in mineral processing. In that sense, this research deals with the use of the hydrophobic Gram-positive Rhodococcus erythropolis bacteria as a possible substitute for synthetic reagents used in haematite flotation. Bacterial growth experiments, using culture media of tryptic soy broth (TSB) and yeast and malt extract with glucose (YMG) separately, showed a greater bacterial density for the first one. In addition, it was observed that the isoelectric point (IEP) of haematite was shifted after biomass interaction, suggesting that the bacterial cells were adhering to the mineral surface. Moreover, bacterial adhesion was higher at acidic pH, which also suggests an electrostatic attraction between the mineral surface and the biomass at this pH range. Microflotation tests were carried out in a modified Hallimond tube achieving a maximum haematite floatability of 83.86% at pH 6. Finally, the kinetics of the process followed a second order model. (Authors)., The use of microorganisms and/or their metabolic products is becoming an attractive alternative in mineral processing. In that sense, this research deals with the use of the hydrophobic Gram-positive Rhodococcus erythropolis bacteria as a possible substitute for synthetic reagents used in haematite flotation. Bacterial growth experiments, using culture media of tryptic soy broth (TSB) and yeast and malt extract with glucose (YMG) separately, showed a greater bacterial density for the first one. In addition, it was observed that the isoelectric point (IEP) of haematite was shifted after biomass interaction, suggesting that the bacterial cells were adhering to the mineral surface. Moreover, bacterial adhesion was higher at acidic pH, which also suggests an electrostatic attraction between the mineral surface and the biomass at this pH range. Microflotation tests were carried out in a modified Hallimond tube achieving a maximum haematite floatability of 83.86% at pH 6. Finally, the kinetics of the process followed a second order model. (Authors).

Zeta potential determinations showed that the isoelectric point (IEP) of beryl is near a pH of 2.7; pretreatment with HCl displaced it to pH 2.3, and with HCl and HF almost to pH 3.7. The presence of metallic cations such as Fe3+, Al3+, Ca2+ and Mg2+ strongly affected the mineral surface potential for both pretreatments. Hallimond tube tests with sodium dodecyl sulphate and sodium petroleum sulphonate collectors, in the absence of the metallic cations, indicated that for HCl-pretreated beryl flotability is significant when pH is below the IEP, while pretreatment with HCl and HF increased flotability in the pH range 2-10. Metal hydroxi-complexes had an activating effect on the mineral and colloidal metal hydroxides were depressants. The adsorption mechanism is similar for all the cations studied., Zeta potential determinations showed that the isoelectric point (IEP) of beryl is near a pH of 2.7; pretreatment with HCl displaced it to pH 2.3, and with HCl and HF almost to pH 3.7. The presence of metallic cations such as Fe3+, Al3+, Ca2+ and Mg2+ strongly affected the mineral surface potential for both pretreatments. Hallimond tube tests with sodium dodecyl sulphate and sodium petroleum sulphonate collectors, in the absence of the metallic cations, indicated that for HCl-pretreated beryl flotability is significant when pH is below the IEP, while pretreatment with HCl and HF increased flotability in the pH range 2-10. Metal hydroxi-complexes had an activating effect on the mineral and colloidal metal hydroxides were depressants. The adsorption mechanism is similar for all the cations studied.