Process Water Chemistry Research Articles

Buffering of pulp pH and its influence on process water chemistry during iron ore flotation

Buffering of pulp pH and its influence on process water chemistry during iron ore flotation

Study of process water recirculation in a flotation plant by means of process simulation

One of the biggest challenges in the mining industry is the need for water management systems that consider production-related issues when the quality of process water is subject to variations. Part of the work required to tackle this challenge is the development of simulation platforms that correlate the quality of the process water to the processing plant performance. In this paper, the application of a previously developed method to include the impact of process water chemistry in the simulation of a flotation plant performance is presented. The water chemistry-dependent plant simulation is then used to investigate the impact of intensified process water recirculation on the flotation plant performance, thus showing the relevance of the previously developed approach to help implementing water-saving strategies in the mineral processing industry.

Water-saving strategies in the mining industry – The potential of mineral processing simulators as a tool for their implementation

As the mining industry is facing an increasing number of issues related to its fresh water consumption, water-saving strategies are progressively being implemented in the mineral processing plants, often leading to variations in the process water chemistry. However, the impact of water chemistry variations on the process performance is rarely known beforehand, thus creating an obstacle to the implementation of those water-saving strategies. To tackle this problem, the effect the different dissolved species present in the process water have on the processing plant performance must be quantified, and this information must be digitalized in a practical and suitable form to be used in mineral processing simulators. To achieve this goal, a methodology to digitalize the influence of the process water composition on the flotation performance is presented in this paper. Using the flotation of a fluorite ore as case study, the relationship between process water composition and the flotation kinetics of that fluorite ore was determined. This relationship was digitalized in HSC Sim, a mineral processing simulator, turning it into a tool capable of simulating the flotation performance under a variety of process water compositions. Finally, the potential of this new tool to help implementing water-saving strategies on the mine site is discussed, and the challenges that need to be overcome in order to apply this tool at industrial scale are being addressed.

The influence of process water chemistry on coal thermoplastic properties

Process water re-use is a common practice in Australian coal preparation plants. It is an effective solution to on-site water scarcity and minimizes environmental impact. This paper investigates the effect of inorganic mineral salts in the process water on the thermoplastic properties of metallurgical coals after a short period of mild oxidation. Two different metallurgical coals were treated with the process water received from a coal preparation plant and exposed to air at ambient temperature. The thermoplastic properties of the samples treated with salt solutions were measured using Gieseler plastometry. The results suggested that the fluidity of coal decreased as the concentration of inorganic salts increased. When different salt solutions were used, the degree of fluidity reduction was found to be similar at the same concentration. Examination of the coal surface with SEM-EDS analysis showed the existence of both sodium and chlorine on the surface of process water treated coal while the surface analysis by X-ray photoelectron spectroscopy (XPS) indicated a relatively insignificant chemical reaction between the inorganic ions present in the water and the coal surface after rinsing the samples. Salts appeared to precipitate on non-maceral matter and act as an inert (non-plastic) additive.

An investigation into the effect of water quality on froth stability

Froth stability plays a major role in determining the mineral grade and recovery in flotation operations, and it depends on the type and amount of both frother and suspended particles. Furthermore, there are other parameters such as quality of the process water which may affect the froth stability. In plant practice, the recycling of process water instead of using fresh water is increasingly being common. However, using recycled water normally leads to building up salts and surfactants in solution. Therefore, the effect of the process water chemistry on froth stability and metallurgical performance is important. In this study, the effect of water quality, including pH, and type and concentration of salts (CaCl2, AlCl3 and NaCl) on froth stability and its relationship with mineral particles zeta potential and slurry viscosity was studied. It was found that the forth stability is higher in the presence of multivalent metal ions. Addition of CaCl2 and AlCl3 considerably increased both froth stability and pulp viscosity. This may be due to bridging effect of polyvalent metal ions between the ore particles.

Partitioning of major and trace inorganic contaminants in fly ash acid mine drainage derived solid residues

Acid mine drainage was reacted with coal fly ash over a 24 h reaction time and species removal trends evaluated. The evolving process water chemistry was modeled by the geochemical code PHREEQC using WATEQ4 database. Mineralogical analysis of the resulting solid residues was done by X-ray diffraction analysis. Selective sequential extraction was used to evaluate the transfer of species from both acid mine drainage and fly ash to less labile mineral phases that precipitated out. The quantity of fly ash, volume of acid mine drainage in the reaction mixture and reaction time dictated whether the final solution at a given contact time will have a dominant acidic or basic character. Inorganic species removal was dependent on the pH regime generated at a specific reaction time. Sulphate concentration was controlled by precipitation of gypsum, barite, celestite and adsorption on iron-oxy-hydroxides at pH > 5.5. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. PHREEQC predicted precipitation of iron, aluminium, manganese-bearing phases at pH 5.53–9.12. An amorphous fraction was observed to be the most important in retention of the major and minor species at pH > 6.32. The carbonate fraction was observed to be an important retention pathway at pH 4–5 mainly due to initial local pockets of high alkalinity on surfaces of fly ash particles. Boron was observed to have a strong retention in the carbonate fraction.

Factors influencing the risk of wildlife cyanide poisoning on a tailings storage facility in the Eastern Goldfields of Western Australia

Patterns of wildlife visitation and interaction with cyanide-bearing tailings slurry and solutions at the Fimiston tailings storage facility (TSF) have been reported in a previously published ecological study. The above-mentioned findings are extended in this paper by the examination of additional wildlife survey data, along with process water chemistry data collected during the same study period. Analysis of the combined results revealed that the primary wildlife protective mechanism in operation was effective management of tailings cyanide concentration. Nevertheless, tailings discharge concentration exceeded the industry standard wildlife protective limit of 50 mg/L weak acid dissociable (WAD) cyanide episodically during the study period. Wildlife that interacted with habitats close to the spigot outlet during brief periods of increased discharge concentration were likely to have been exposed to bioavailable cyanide at concentrations greater than the industry standard protective limit. However, no wildlife deaths were recorded. These results appear to support the hypothesis that hypersalinity of process solutions (unique to the Kalgoorlie district of Western Australia) and a lack of aquatic food resources represent secondary protective mechanisms that operated to prevent cyanide-related wildlife mortality during the project. The proposed protective mechanisms are discussed in the context of their potential application as proactive management procedures to minimise wildlife exposure to cyanide.

Anionic flotation of high-iron phosphate ores—Control of process water chemistry and depression of iron minerals by starch and guar gum

The fatty acid flotation of a difficult-to-float igneous phosphate ore (26.2% P 2O 5, 15.4% Fe 2O 3) was investigated through batch flotation tests in the presence of soda ash. The poor flotation of this otherwise high quality ore was attributed to very high concentrations of calcium and sulfate ions (about 1000 and 2000 mg/L, respectively) found in process water, which indicated that the flotation pulp was saturated with respect to calcium sulfate. Despite the very high concentrations of calcium, the flotation results and pulp titration tests as a function of soda ash dosage showed that high concentrate grades (> 36% P 2O 5) and phosphate recoveries (~ 80%) could readily be achieved straight from such a high-calcium environment using pulp pH and conductivity as parameters for controlled addition of soda ash, especially during a continuous plant process. The main role of soda ash was to precipitate calcium and other interfering cations from the pulp thus allowing the tall oil collector to interact with the phosphate components. A comparative study of corn starch and guar gum as iron depressants for two phosphate ores varying in mineralogy of iron minerals (high-siderite and low-siderite, and various oxides) showed that guar gum was a more effective iron depressant than starch in terms of P 2O 5 grades of the concentrates. However, longer flotation times were necessary in the presence of higher doses of guar gum in order to achieve high P 2O 5 recoveries. The depressant performance of guar gum was superior to that of starch especially for the high-siderite ore.

Effect of bitumen composition and process water chemistry on model oilsands separation using a warm slurry extraction process simulation

Variability in ore composition and process parameters is known to affect bitumen recovery from natural oilsands. In this work, we extend our earlier studies with model oilsands (MOS) systems to investigate the effects caused by the presence of asphaltene and divalent cations on the interaction between bitumen and silica particles. The absence of both asphaltene and fines was found to have significant effects on bitumen recovery. With a typical oilsands, addition of small amounts of caustic improves recovery but overdosing causes a drastic loss of yield through bitumen emulsification. Without asphaltene and in the presence of fines, the typical drop in bitumen recovery above pH 10 did not occur, indicating that the source of emulsifying agents had been eliminated. With deasphalted bitumen, recovery in the absence of silica fines was very poor at all NaOH dosages. The strong, negative effect of divalent cations on “normal” bitumen recovery was almost completely eliminated when asphaltene was absent.

Effect of process water chemistry and particulate mineralogy on model oilsands separation using a warm slurry extraction process simulation

Variability in ore composition and process parameters is known to affect bitumen recovery from natural oilsands. In this work, we extend our earlier investigations with model oilsands systems (MOS) to determine the effects of calcium, magnesium and bicarbonate ion concentrations in the process water and their interactions with ‘active’ solids such as: kaolinite, montmorillonite and ultra-fine silica. Our results demonstrate that solids mineralogy and decreasing particle size produce negative outcomes on bitumen recovery related to concomitant effects on bitumen droplet size during flotation. In some cases, certain process water chemistries were found to restore recovery, but clay concentration was the key factor. Naturally acidic oilsands are known to give poor bitumen recoveries. An MOS prepared with connate water at pH 2 responded in the same way. Comparison with a typical oilsands showed no significant differences in middlings pH and the large, negative effect on bitumen recovery was not reversed by higher caustic loading during separation. This result may be caused by irreversible co-flocculation of bitumen and mineral particles during preparation of the MOS and may reflect similar behavior in comparable natural samples.

Bitumen recovery from model systems using a warm slurry extraction process: effects of oilsands components and process water chemistry

Natural oilsands is a complex mixture of sand, clay, bitumen and connate water that can vary markedly from one sample to another. Also, oilsands processability is known to depend on composition and process water chemistry. Because these variables are hard to control, the effect of an individual oilsands component on bitumen recovery is difficult to determine. Here, we carry out a series of systematic screening experiments with model oilsands (MOS) to determine the effects of system components and water chemistry on bitumen recovery using a warm slurry extraction process. Atmospheric topped, blended or deasphalted bitumen were used at a constant level of 10-wt% in the preparation of the model systems. The solids components tested included: different size fractions of silica sand, and several commercial clay minerals, including illite, montmorillonite and kaolinite. Clay concentrations were varied up to 5-wt% of the total solids. Anions and cations at concentrations comparable to those in process water from a commercial oilsands extraction plant were also evaluated. Bitumen recovery results from these screening tests were compared with those for a base case, or standard, MOS mix comprising 10-wt% atmospheric topped bitumen, 21-wt% silica fines and 5-wt% deionized water at pH 8; coarse silica sand provided the balance to 100-wt% of solids, or 64-wt% of the MOS. Recovery results for the different screening test variables were classified into three categories: (1) Bitumen recoveries comparable to those for the standard MOS, i.e. size of coarse solids, bitumen type, sodium, chloride and sulfate ions. (2) Decreased bitumen recovery, reversible by addition of more NaOH, i.e. size/amount of fine solids and illite. (3) Bitumen recovery that could not be reversed, i.e. synthetic hydrophobic coarse solids, montmorillonite, kaolin, calcium and magnesium ions.

RO pre-treatment - injecting a little chemical control and management

The successful longevity of RO plants and membranes depends critically upon both the design and operation of the pre-treatment systems and the optimisation of membrane management programmes especially in the larger plants. The construction of large RO plants by traditionally “Evaporation” orientated engineering companies has often resulted in a concentration on the engineering properties but with an underestimation of the fundamental importance of chemical and biological processes to the successful design and operation of RO plants treating both brackish and sea waters. The complex and often not well understood interactions between the modified chemical, physical and biological constituents of feed waters, which so often are the cause of membrane fouling episodes, lack the inherent robustness, accuracy and familiarity of the more accustomed engineering variables of pressure, flow and temperature. This paper describes how successful feed water pre-treatment design, control and membrane management depends on understanding the complex physical, chemical and biological interactions occurring at each plant unit process within an overall context of process water chemistry, to minimise fouling problems and prolong membrane longevity.