Yongjun Peng

Control of grinding conditions in the flotation of chalcopyrite and its separation from pyrite

Abstract A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on chalcopyrite flotation and chalcopyrite separation from pyrite. The mechanism of galvanic interaction between minerals and grinding media was investigated by ethylene diamine-tetra acetic acid disodium salt (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) measurements. Chalcopyrite flotation was strongly dependent on both iron oxidation species and metal deficiency on the chalcopyrite surface. Iron oxidation species from grinding media played a dominant role in depressing chalcopyrite flotation, while metal deficiency from chalcopyrite oxidation improved chalcopyrite flotation. Therefore, chromium grinding medium produced a higher chalcopyrite recovery than mild steel grinding medium while gas purging during grinding had little effect on chalcopyrite flotation. Chalcopyrite separation from pyrite was affected by the activation of pyrite flotation by copper species dissolved from chalcopyrite. Grinding media had a large effect on the reduction of copper(II) to copper(I) on the pyrite surface. The reducing grinding condition generated by mild steel medium favoured formation of copper(I) sulphide phase, which resulted in high pyrite activation. Thus, chromium medium produced better chalcopyrite selectivity against pyrite than the mild steel medium.

Control of grinding conditions in the flotation of galena and its separation from pyrite

Abstract A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on galena flotation and galena separation from pyrite. The various reactions occurring on the mineral surface were investigated by a range of techniques, including OH − addition to maintain the grinding pH, ethlenediamine tetra acetic acid disodium salt (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and Time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements. Galena flotation and galena separation from pyrite were strongly dependent on the metal oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, while lead oxidation species activated pyrite but had little effect on galena. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation to be controlled. Aeration during grinding interfered with oxygen reduction occurring on the mineral acting as the cathode, as a result of galvanic interaction, and influenced the flotation of that cathodic mineral. Oxygen purging during grinding depressed galena flotation in single mineral experiments but increased galena selectivity against pyrite.

The development of a composite collector for the flotation of rutile

Abstract A study was carried out to find a replacement for benzyl arsenic acid (BAA) that was used in the rutile flotation circuit of a hard rock rutile mine in China. Several types of oxide collectors were tested, including sodium oleate, sodium laurate, sodium dodecyl sulphate, amino acids, diphosphonic acid and styryl phosphonic acid. It was found that styryl phosphonic acid (SPA) was the most effective, and that an aliphatic alcohol (e.g., octanol) was required to maintain the effectiveness of SPA. However, octanol was insoluble in water. The composite collector that was mixed with SPA and octanol had to be well emulsified before addition to flotation pulp. Poorly emulsified composite collectors destroyed flotation froths. Several surfactants were tested as emulsifiers and one was found to have the least adverse effects on the selectivity of the composite collector. By using the composite collector that contained SPA, octanol and the emulsifier, a rutile rougher concentrate assaying 71.3% TiO 2 was floated at 81.6% recovery from a feed containing 8.78% Ti0 2 in a single stage rougher flotation.

Towards prediction of oxidation during grinding I. Galena flotation

The degree of oxidation during grinding and its effect on galena flotation were studied using a specialised mill which permitted chemical conditions during grinding to be controlled. It was found that iron oxidation species derived from the grinding medium played a dominant role in galena flotation. The amount of hydroxide consumed to maintain the grinding pH at a constant value depended on the production of iron oxidation species. Linear relationships were obtained between the amount of hydroxide consumed to maintain a constant grinding pH and the production of iron oxidation species as well as galena recovery. These relationships should eventually permit oxidation during grinding and galena flotation to be predicted.

Dissolution of fine and intermediate sized galena particles and their interactions with iron hydroxide colloids.

Dissolution of fine (-10 microm) and intermediate (+10-53 microm) galena particles was studied in the presence and absence of iron hydroxide colloids at pH 9 with nitrogen and oxygen purging. X-ray photoelectron spectroscopy (XPS) measurements and ethylene diamine-tetra acid (EDTA) extraction of the galena particles after dissolution indicate that galena dissolution is strongly dependent on particle size. Fine galena particles produced a much higher amount of lead hydroxide species per surface area than intermediate galena particles. Gas purging only affected galena dissolution slightly. More iron hydroxide colloids adsorbed on fine particles. Zeta potential measurements indicate that galena dissolution enhances the adsorption of iron hydroxide colloids due to the electrostatic attraction between lead hydroxide products and iron hydroxide colloids at pH 9. This explains the stronger affinity of iron hydroxide colloids to fine galena particles than intermediate galena particles. This study has an important implication in sulfide flotation where iron hydroxide colloids play a dominant role in mineral depression.

Froth stability of coal flotation in saline water

Abstract The objective of this study was to identify a practical solution to mitigating over-stable froth problems in fine coal flotation in saline water. The effect of coal particle size, water quality and chemical reagents which can be manipulated in flotation plants, on the froth stability and coal flotation performance was investigated. It was found that froth stability was dependent on the coal particle size, the proportion of process water mixed with de-ionised water and the dosage of the collector or frother. Mixing coarse coal particles with fine coal, diluting process water, and reducing collector or frother dosage all significantly decreased the froth stability. However, only the reduction of reagent usage was recommended as a sound strategy since it did not negatively impact the coal flotation performance while eliminating the over-stable froth problems.

Effect of feed preparation on copper activation in flotation of Mt Keith pentlandite

Abstract In this work, the effect of copper sulphate on the flotation of Mt Keith pentlandite ores was studied. As Mt Keith operates separate size flotation circuits, e.g. slime (−8 μm), fine (−25 μm) and coarse (−160 μm) circuits, tests were conducted on streams of different particle size distributions prepared with the use of cyclones. The flotation response with and without the addition of copper sulphate was examined, first, on feed streams prepared by a laboratory grinding mill and cyclone and, second, on streams collected directly from the plant. It was found that copper sulphate had an adverse effect on flotation performance when the flotation feeds were prepared in the laboratory. In the flotation of slime-fine fractions that combined slime and fine particles, the addition of copper sulphate depressed nickel flotation while increasing gangue entrainment. In the flotation of coarse fractions, the addition of copper sulphate depressed nickel flotation without affecting gangue entrainment. However, when samples were collected directly from the plant streams and floated in a laboratory flotation cell, the addition of copper sulphate increased nickel recovery without affecting gangue entrainment in the flotation of slime, fine and coarse fractions. To explain this discrepancy, pulp chemistries in the two different types of tests were compared. It was found that the plant mills at Mt Keith produced a much more reducing grinding environment than the laboratory mill. This might contribute to the completely different behaviour which copper sulphate exhibited on flotation performance. This study also demonstrates the importance in considering plant pulp chemistry during research development in a laboratory.

Managing clay minerals in froth flotation—A critical review

ABSTRACT Clay minerals are widely present in various ore deposits as gangue minerals. The processing of high-clay-content ores is becoming a significant challenge for the mining industry owing to the poor flotation performance caused by the presence of clay minerals. Different types of clay minerals are typically present in ore bodies, and they cause several detrimental effects to flotation that require different treatments. In this article, a comprehensive review of the studies on understanding and mitigating the negative effects of clay minerals in flotation is presented. It starts with a review of the classification and structures of clay minerals commonly occurring in ore deposits and their properties that determine the behavior of clay minerals in flotation. It is followed by a critical review of two main negative effects of clay minerals on flotation, the recent research findings mainly from The University of Queensland group. The first negative effect is the coating of clay minerals on the surface of valuable minerals that decreases the floatability of valuable minerals. The second negative effect is the formation of network structures in the slurry. Depending on the type and strength of the network structure, it can cause either high pulp viscosity or increased gangue entrainment, which reduces the flotation recovery and flotation product grade, respectively. In this section, the mechanisms and key factors behind each negative effect are presented and critically discussed. Then, the approaches and techniques developed to mitigate the different negative effects of clay minerals are reviewed. To conclude, future directions for a more complete understanding of mechanisms and problem solving are recommended.

Effect of froth stability on dewatering of coal flotation concentrates

Abstract This study was conducted to investigate the effect of froth stability on coal filtration and dewatering characteristics by comparing the filtration and dewatering responses of flotation concentrates and unfloated coal slurries. The results show that high froth stability originating from a flotation process has a negative impact on the filtration and dewatering of flotation concentrates. In this study, the flotation of fine coal using saline water produced a highly stable froth with a high air recovery resulting in a short cake formation time and a high final cake moisture content when the flotation concentrate was dewatered. The air bubbles entrained in the flotation concentrate blocked and resisted the flow of water during filtration and dewatering. The moderately and weakly stable froths produced from the flotation of fine coal using deionised water and coarse coal using saline water respectively did not affect the filtration and dewatering process.

Dry separation of iron minerals from low-grade coal-series kaolin

Dry separation of iron mineral from low-grade coal-series kaolin in Hubei Province of China was investigated. The structure and chemical composition of the kaolin ore were determined by X-ray diffraction (XRD) and X-ray Fluorescence (XRF) analyses. The narrow particle size range classification, dry magnetic separation and calcination were carried out to evaluate the particle size distribution, and the relation between the content of iron and the whiteness. Experimental results revealed that the highest content of iron (3.70%) in kaolin ore was in the particle size range from 60 to 74 μm, and pyrite was the main occurrence of iron in the kaolin ore. Dry magnetic separation showed that the removal rate of iron in kaolin ore could be increased obviously after calcination, and the rate of iron removal was 60% in the particle size range from 60 to 74 μm. As pyrite can be transformed into hematite through calcination, thermodynamic studies and XRD analysis showed that the maximum content of hematite was obtained at 900 °C, which would be more beneficial to magnetic separation.