R.W. Smith

Overview of flotation as a wastewater treatment technique

The treatment of aqueous or oily effluents is one of the most serious environmental issues faced by the minerals and metallurgy industries. Main pollutants are residual reagents, powders, chemicals, metal ions, oils, organic and some may be valuable (Au, Pt, Ag). The use of flotation is showing a great potential due to the high throughput of modern equipment, low sludge generation and the high efficiency of the separation schemes already available. It is concluded that this process will be soon incorporated as a technology in the minerals industry to treat these wastewaters and, when possible, to recycle process water and materials. In this paper, the use of flotation in environmental applications is fully discussed. Examples of promising emerging techniques and devices are reported and some recent advances in the treatment of heavy metal containing waters and emulsified oil wastes are discussed.

Biosorption of metals onto plant biomass: exchange adsorption or surface precipitation?

Heavy metal ions readily adsorb onto the nonliving biomass of many aquaphytes. Further, in many cases the metal ions can be readily desorbed from the biomass by use of a suitable eluting agent. It has been shown in certain cases, at least, that the biomass can be subjected to a number of loading and elution cycles without the biomass losing its adsorption capacity. It has been widely reported that the adsorption is through a specific ion exchange mechanism and a number of researchers have shown experimental evidence supporting such a mechanism. However, there is also evidence that the adsorption is through simple surface precipitation of metal hydroxide species. The present study examines some of the existing data on adsorption of metal ions onto aquaphyte biomass and attempts to evaluate which mechanism is the more likely.

Adhesion of two bacteria onto dolomite and apatite : Their effect on dolomite depression in anionic flotation

Abstract Bacteria can adhere to mineral surfaces and affect subsequent flotation of the minerals. In the present study, the adhesion of Bacillus subtilis and Mycobacterium phlei onto dolomite and apatite was studied by sorption measurements and scanning electron microscopy. The effect of the microorganisms on the oleate flotation of the minerals was then compared at several different pH values. It was found that both B. subtilis and M. phlei adhered to dolomite more readily than onto apatite at acidic and near neutral pH values . At more basic pH values B. subtilis adheres more readily onto and remains a better depressant for dolomite than for apatite. However, at basic pH values, M. phlei adsorbs more onto apatite than onto dolomite with the result that it is a weaker depressant for dolomite, but a stronger depressant for apatite than B. subtilis . The differences in adsorption characteristics are attributed to the different surface characteristics of the two bacteria species and of the two minerals. Both possess acidic isoelectric points. However, B. subtilis has a greater affinity for Mg(II) ions than does M. phlei . Thus, B. subtilis should adsorb more strongly onto dolomite through Mg sites than M. phlei . M. phlei , however, has a more hydrophobic surface. The result is that both species adsorb onto dolomite and function as dolomite depressants and also function as apatite depressants, albeit as weaker depressants. The net results show that, while both function as depressants in anionic collector flotation of dolomitic phosphate ores, B. subtilis functions as the stronger depressant, especially for dolomite. Implications in the anionic flotation of apatite from dolomite are discussed.

KINETIC ASPECTS OF AQUEOUS ALUMINUM CHEMISTRY : ENVIRONMENTAL IMPLICATIONS

Abstract Aluminum is a common constituent of the earths crust and is present in many rock and soil forming minerals. In spite of its abundance Al(III) usually is not very soluble in water. However, strong mineral acids, such as may be present in rainfall, can solubilize some of the aluminum. On becoming solubilized the Al(III) can be present in the natural water environment in a number of forms. The speciation of Al(III) is complex and depends not only on the aqueous environment itself (inorganic and organic ions present, the solids the water is in contact with, inorganic and organic) but also on the past history of the Al(III) containing water. An attempt is made to predict the fate of Al(III) is complex and depends not only on some manner, such as through the precipitation of strong inorganic acid containing rain on various diverse landscapes. The past history of the Al(III) containing water, the effect of pH rise, the presence of inorganic and organic dissolved substances and the presence of various minerals and organic materials are considered in the predictions.

Sorption of Hg(II) by Potamogeton natans dead biomass

Abstract The sorption of Hg(II) from aqueous solution onto the dead biomass of the aquaphyte Potamogeton natans was studied. The uptake was studied by placing the Hg(II) solutions into beakers containing various concentrations of biomass. Factors influencing the sorption process such as reaction time, initial pH value of the treated solution, and initial concentration of metal ions were examined. Chemical and instrumental analyses including atomic absorption, electron microscopy and X-ray energy dispersion analyses were used to elucidate sorption mechanisms. It was found that, although sorption of Hg(II) took place over the entire biomass surface, there were spots on the surface where apparent multilayer sorption of Hg(II) occurred. The maximum uptake of Hg(II) by P. natans biomass is about 180 mg/g biomass. The minimum concentration of Hg(II) in solution that can be achieved appears to be limited to about 4–5 mg/l.

A Dried Hydrophobic Aquaphyte as an Oil Filter for Oil/Water Emulsions

Abstract In the present study, dead biomass derived from a hydrophobic aquatic plant, a Salvinia sp. found in Southern Brazil, was studied as an oil filter for oil/water emulsions. The performance of the Salvinia sp. biomass as such was compared to that of a processed peat (Peat Sorb) that is sometimes used as a sorbent for oil. In the utilization of the Salvinia sp. and Peat Sorb as filters for oil in oil/water emulsions the results of two equal tests were averaged in order to verify the reproducibility of the experimentation. In the experiments the emulsion was passed through the filters until saturation of the filter was indicated by the appearance of oil in the filtrate (breakthrough). For Salvinia sp., the average amount of emulsion passed through the filter until breakthrough was 18.7 l containing 10.61 g oil. The amount of oil retained was 9.53 or 1.33 g oil/g biomass. Thus, 90% of the oil in 18.7 l emulsion was retained by the biomass. The tests using Peat Sorb were performed under the same conditions as for the aquaphyte biomass. The average amount of emulsion passed through the filter until breakthrough was 4.0 l containing 2.68 g oil. The amount of oil retained was 1.66 or 0.26 g oil/g Peat Sorb. Thus, the Peat Sorb retained 62% of the oil in 4.0 l emulsion. The superiority of the Salvinia sp. for removing oil from such emulsions, since the surface areas of the two materials are similar, appears to be due to the hydrophobicity and the hair like projections of the surface of the aquaphyte biomass.

Microorganisms as chemical reagents: The hematite system

Abstract Microorganisms can function as flocculating agents, flotation modifiers and flotation collectors. Thus, they can take the place of chemical reagents in mineral processing and hydrometallurgy operations and, therefore, can be themselves considered as reagents. For example, a microorganism should function somewhat as a chemical flocculant if it is to some degree hydrophobic and can attach itself in some manner, such as though electrostatic interaction, to the fine mineral particles to be flocculated. In addition, hydrophobic microorganisms should render a hydrophilic mineral surface somewhat hydrophobic if they attach themselves to the mineral surface. A previously non-floatable mineral can in this manner be rendered floatable. The present paper investigates the principles of the use of a hydrophobic, highly negatively charged, bacterium, Mycobacterium phlei , as a flocculating agent for finely divided hematite suspensions and as a flotation collector for hematite.

Mechanisms of Dodecylamine Flotation of Quartz

Primary monoamines have been long used and studied as flotation collectors for quartz. In the past several mechanisms have been proposed to explain the manner in which the amines adsorb onto and render the mineral hydrophobic and, thus, floatable. From past data and proposed mechanisms and reinterpreting some of the past data it appears that somewhat different mechanisms account for amine function at different pH values. At low pH values the amine ions apparently adsorb as individual ions through coulombic interaction between the ion and the quartz surface. The surface coverage of amine ions is not great and only limited flotation takes place. As pH is raised adsorption of individual ions (monomers and dimere) increase. Thus it is suggested that at higher pH values, provided the Krafft lemperature is not exceeded (26° C for dodccylammonium chloride), the adsorption of ions increases with pH to a point where the amine solubility limit is exceeded within the quartz-solution interface. Surface precipitation ...

Eichhornia crassipes as biosorbent for heavy metal ions

Abstract Eichhornia crassipes approaches being a scourge in many parts of the world, choking waterways and hindering transport upon them. At the same time it is known to readily abstract heavy metal ions from water and, thus, aids in the removal of heavy metals found in such waters. This paper considers the possibility of using dried parts of the plant as an inexpensive adsorbent for the removal of heavy metals from contaminated chemical and mining industry waste waters. In particular the root of the plant was found to be an excellent accumulator of divalent heavy metal ions from solution although the entire biomass of the plant was also found to be a good sorbent for these ions. It is also suggested that the dried biomass of the plant might be placed in simple bags and used in a very low cost metal ion removal system.

Dolomite depressants in the flotation of apatite and collophane from dolomite

Abstract A number of different chemical substances were evaluated for their ability to depress dolomite in the flotation of apatite and collophane from dolomite. Carboxymethyl cellulose was found to be the best depressant and citric acid and naphthyl anthyl sulfonates were found to be good depressants for dolomite. None of these substances significantly depressed apatite or collophane. EDTA was found to be a dolomite activator rather than depressant. The other chemicals studied had little effect on either dolomite or apatite flotation.