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By Vladimir G. Kochnev

An innovative AG and SAG technology aimed to be applied in grinding of ores and in the production of construction materials is described. A novel design of a cantilever-type mill capable to operate in autogenous, semi-autogenous and ball grinding mode ensures easy delivery and installation even in remote areas, and low capital and operating costs. Results of the tests of the new heel-shaped liners performed by TTD jointly with ALROSA, MINTEK and Anglo-American Corporation are reported. The approach includes also a novel discharge grid design and a technique of treating the material of critical size. These innovations make grinding in AG and SAG mills dramatically more effective, with an increase in the throughput rate and a reduction in power consumption ranging from 1.5 to 2 times.

Jan 1, 2003

By G. A. Wierink

This paper discusses a new method to increase flotation recovery. As known from literature, fine and coarse particles have different flotation rate constants, hydrodynamic behaviour and require different reagent regimes. The device discussed allows separate processing of finer and coarser slurry by extraction of a third stream, carrying finer slurry, from the flotation cell. By separate treatment of fine and coarse slurry operational conditions and so flotation recovery for both may be optimized more efficiently. Extraction and classification of the third stream is accomplished by low speed centrifugation and Taylor-Couette flow separation. This Dual Outlet Device (DOD) can be installed in a traditional flotation cell without need for equipment replacement. In order to asses different design options for the DOD a transparent laboratory scale model was built. For this scale model Computational Fluid Dynamics (CFD) simulations using the RANS k-e and LES turbulence models were performed. Essential insight in the dominant flow systems relevant to optimal operation of the DOD was obtained from the CFD simulations and flow visualization tests with the laboratory scale model. Based on these findings a number of configurations were investigated at pilot plant scale in a 5 m3 Outokumpu flotation cell. The results of the pilot plant study show that utilization of the DOD provides a method for in-cell control over particle size distribution in the slurry. Use of the DOD in a flotation cell may enhance flotation recovery and decrease flotation reagent consumption significantly, against marginal investment and operation costs.

Jan 1, 2014

By Glaser. C., J. Balz, F. Logsch, R. Heiduschke, M. Leiker, P. Ay

The treatment of iron-hydroxide-containing water from ground water and surface water is achieved by a combination of the process steps of flocculation and subsequent mechanical dewatering. The aim is to create solid pellet structures by extending the structure forming flocculation process with a build-up pelletizing process which can be transferred directly into a drying unit. A Taylor-Couette-reactor (diameter of the inner cylinder – 40 mm, gap width – 5 mm) was used for these experimental studies. To produce the necessary flow profile the inner cylinder was rotated at a speed of 230 rpm. The iron hydroxide-containing suspension (dry matter content: 2 mass %) was added simultaneously with the addition of a cationic high-molecular flocculant in various flocculant dosages and residence times of 5 to 15 min. The pellets were examined for parameters such as geometric dimensions, dry substance content and dewatering behaviour. As the results show, there is a direct relationship between the residence time and the geometric dimensions of the pellets. After a residence time of 5 min, round pellets with an average diameter of 6 mm were formed. With an increase in the residence time up to 15 min, a compaction of the pellets could be observed, which resulted in an increase in the dry substance content of 8.0 to 11.2 mass % on average. After completion of the pelletizing process, the pellets were mechanically dewatered by filtration. By applying this innovative wet pelletizing of iron-hydroxide containing suspensions in a Taylor-Couette-reactor, it is possible to carry out the process of flocculation combined with the pellet formation with simultaneous pellet compaction in a single process step. The resulting pellet structures are distinguished from conventional floc structures by an improved water discharge capacity. After classification the pellets can be marked directly as easy-to-handle bulk material, suitable as feedstock in percolation columns for the purification of contaminated fluid streams

Jan 1, 2018

By Rainer M. Lotzien, Michael J. G. Battersby, Jan Kleefeld, Julian V. Brown, Rainer M. Imhof

A new flotation system has been developed to improve the generally slow separating differentials of fine bubbles and fine particle suspensions. The new technology is based on established pneumatic flotation designs called Imhoflot which use intensive in-line pre-aeration to aerate the flotation pulp prior to its introduction to the separating cell. In the new system (see figure 1) this separation is speeded up dramatically by the introduction of centrifugal motivation in the separating vessel, without the use of internal moving parts. The design focuses on providing increased differential forces on buoyant mineralised bubbles and hydrophilic fines. The commercial benefit to industry is much reduced residence time, less than 30 seconds, which offers considerable cost savings in equipment and infrastructure.

Jan 1, 2003

By Matt Kilburn, Liming Lu, Steve Suthers, Alexander Edenton, Rodney Smyth, Matt Adam

"Magnetite concentrate is naturally good for pelletising. However, due to the depletion of reserves of traditional high grade hematite iron ore worldwide, the usage of magnetite concentrate in sintering is expected to increase substantially. Magnetite concentrate is typically high in Fe grade and releases extra heat when oxidised to hematite. This will not only improve the quality of agglomerates produced, but also have a potential beneficial impact on the fuel consumption of the agglomeration process. There are an increasing number of magnetite projects currently being considered and developed. However the concentrates from some of these projects are too coarse as pellet feeds and much finer and denser than normal sinter feeds. Accordingly, special strategies are required in order to utilise the coarse magnetite concentrates at high proportions in pelletising and sintering. This paper discusses various raw material preparation technologies and blending optimization methods demonstrated to be effective for improving the sintering and pelletising performance of coarse magnetite concentrates. Pre-granulation and addition of binders, such as hydrated lime, were found to be particularly efficient in recovering the sintering productivity of sinter blends containing magnetite concentrates. In pelletising, HPGR (High Pressure Grinding Rolls) grinding enabled production of good quality pellets from 100% magnetite concentrates and optimized blends containing up to 70% magnetite concentrates also formed good pellets.INTRODUCTION Magnetite concentrates are often used as feed materials for pellet plants or sinter plants depending on their grades and grain sizes. To achieve the required quality of green and fired pellets, the concentrates often need to be ground very fine (80% passing 38- 45 m), which inevitably consumes a great amount of energy. Therefore, efficient grinding processes are required to reduce the amount of energy consumption needed to achieve the sizing and chemical specification of pellet feeds. The use of magnetite concentrates in sintering has the potential to improve sinter chemistry, which is deteriorating over time due to the slowly decreasing grade of direct shipping iron ores around the world (Yang and Mathews, 1997; Yang and Witchard, 1998, Yang and Davis, 1999; Yang 2005). However, methods are required to allow the utilisation of high levels of concentrates in sintering while maintaining productivity and sinter quality (Han and Lu, 2017)."

Jan 1, 2018

By Tomasz Niedoba

Coals occurring in nature are characterized by various properties. According to Polish norms, the classification of coals taking into consideration their calorific value contains coals from type 31 (flaming coal) until type 43 (meta-anthracite). The samples of coal of type 31 were taken for investigation. To this purpose, the approximations of ash contents and density distribution functions were done for this coal type (determination of marginal distribution functions). They were the basis for application of so-called Morgenstern distribution functions to approximate the function Z=L (?), where Z is ash contents and ? - coal density. Then, the comparison between obtained results was performed and the results were statistically evaluated. They are the basis for the further research of other types of coals.

Sep 1, 2012

By Ghislain Bournival, Seher Ata, Yesenia Saavedra Moreno

"In froth flotation, frothers are commonly added to the pulp to modify the interfacial properties of bubbles. These properties may be modelled using commercial software packages. The volume of fluid (VOF) method was used to track the interface motion during the post-rupture oscillation of the newly formed bubble. The aim of this research was to provide an insight into the modelling of viscoelastic phenomena through the coalescence dynamics of two bubbles in solutions of various surface tensions using a three-dimensional computational study. Different surface tensions were used to simulate changes in methyl isobutyl carbinol (MIBC) concentration. The computational results were evaluated by comparing the oscillatory motion of the newly formed bubble for the different MIBC concentrations. For known MIBC concentrations, the deviations of the computational damping constants from the experiments were quantified, revealing possible deviations in the VOF surface tension model. In addition, the analysis provided insight into the flow patterns of the fluids and the effect of frother concentration on the velocity magnitude in the liquid and air phases. This analysis provided a further understanding of coalescence dynamic and post-rupture oscillation in froth flotation. Such a process is believed to affect the stability of particles at the interface due to the release of surface energy when the bubble surface is reduced.INTRODUCTIONIn froth flotation, bubble coalescence is an important phenomenon that is highly dependent on the interfacial properties of the liquid film between bubbles. It is known that the frother adsorption at the liquid-air interface changes the interfacial properties, resulting in an increase of surface elasticity and reduction of surface energy (Pugh, 2016). However, in a two-phase system, it is the frother type, concentration, frother molecule conformation at the interface and viscoelasticity properties that dictate film stability (Pugh, 2016). The viscoelasticity phenomena can be explained in terms of surface viscosity, which quantifies the energy dissipation at the interface and surface elasticity that represents the energy absorbed at the interface as result of bubble oscillation (Pugh, 2016). In the case of systems stabilized by nonionic frothers, it has been shown that surface forces alone do not account for film stability, but the viscoelasticity represents the ability to damp external disturbances in the thin film separating the bubbles and prevent coalescence (Santini et al., 2007)."

Jan 1, 2018

By Achilles Dutra, Everton Santos, José Oliveira

The beneficiation of phosphate ores by froth flotation is the most efficient process used to separate apatite from gangue minerals like calcite, dolomite and quartz. However, the similarity of surface properties between apatite and calcite generally lead to non-selective adsorption of reagents, rendering the selective separation of these minerals a worldwide problem. The phosphate deposit of Itataia, State of Ceará, Brazil, studied in the present work, presents a complex mineralogical composition having uranium associated with the apatite mineral. The main gangue minerals are calcite and quartz. The bulk flotation of apatite and calcite with anionic collectors in an alkaline medium followed by the selective flotation of calcite at pH 5.5 using phosphoric acid as well as citric acid as depressant have been suggested for this ore. This paper presents the results of contact angle measurements obtained using jojoba oil, a natural reagent composed mainly of gadoleic acid (C20:1) and long-chain fatty alcohols (eicosenol and docosenol), as an alternative collector for the selective separation of apatite and calcite minerals. The hydrophobicity studies were carried out using a computer controlled contact angle goniometer. Additionally, the collector adsorption was evaluated via electrophoretic mobility and FTIR measurements. The results indicated that a high selectivity can be obtained by using jojoba oil as collector in a slightly acid pH range, without the use of depressant. The best results were achieved with a jojoba oil concentration of 200 mg.L-1 at pH 6.5, where the apatite was fully hydrophilic and calcite showed a high hydrophobicity (? > 60 º).

Jan 1, 2014

By Cesar Gomez, Jaime Álvarez, Lisette Wen

Laboratory mechanical flotation cells are extensively used in mineral processing for running batch flotation tests with a variety of purposes, for example assessing feed characteristics, determining flotation kinetics, or testing of new reagents and procedures. It is known that the results obtained depend on the operation mode, self-aerated or forced-air, and on the operating conditions selected for the test, in particular impeller speed and gas flow rate. These different results are a consequence of changes in size distribution of the generated bubble population and its remarkable evolution when frother is added; variations in bubble size affect the bubble surface area flux (BSAF), a variable which correlates with particle collection. Results of a two-phase (air-water) test program designed to measure bubble size for a variety of combinations of impeller type and speed, gas flow rate, frother type and concentration, and cell volume, demonstrated the wide range of BSAF with which the cell can be operated. The results obtained in this work demonstrated that gas dispersion in a forced-air lab flotation machine is significantly affected by the characteristics of the impeller/cell geometry combination in use, and the operating conditions selected. Operating conditions must be carefully selected and maintained during the test to ensure consistent results, in particular when frother concentrations below 20 ppm are used, because frother concentration in the cell will decrease as flotation progresses as a consequence of frother partitioning to the concentrate.

Jan 1, 2014

By Marco Le Roux, Martha Van Rensburg, Quentin Campbell

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25 - 55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal.

Jan 1, 2014

By L. A. Vaisberg, E. V. Shishkin, S. V. Kazakov

"This research is targeted at finding solution to the problem of reduction of specific energy consumption during disintegration of solid materials with the help of machines, operating in a quasiresonant mode. The objective of the research is the development of an energy-saving method of disintegration of supestrong rock and by-products on the basis of vibrational units with two movable crushing elements, operating in a rigorous synchronous-antiphase mode without stringent kinematic links. In the course of investigations a mathematical analysis of the dynamics of vibrational units was performed to determine required mechanical parameters, allowing for adjustment of the machine actuating elements to high-frequency synchronous-antiphase oscillations in the quasiresonant frequency range. As a result of performed pilot tests, the reliability of desktop studies was confirmed and the dependency of process parameters on the machine regulated parameters in the quasiresonant frequency range was identified. The analysis of obtained data showed that during machine operation with cone-shaped crushing elements in the quasiresonant frequency range, the yield of the high-quality finished product (WFA grits of -3+1 mm grain size class) in one pass reaches 35%, whereas the form of the particles corresponds to the grain form with sharp edge. The quasiresonant operation mode of the vibrational unit with two freely suspended crushing elements (without stringent kinematic links) provided substantial reduction of energy intensity during crushing down to 0.16 kWh/t, which shows reduction of power consumption for crushing by more than 15% compared to conventional equipment.INTRODUCTION The most common and energy-consuming processes in the mining industry are the crushing and grinding of various solid materials. Such large energy costs are due to the fact that the capabilities of the existing crushing and grinding machines are based on traditional methods of destruction, and are limited by their kinematic features, which do not allow to reduce the energy intensity of processes, to lower the irreversible loss of useful components, to improve the quality of marketable products. In connection with the foregoing, the task of energy costs reducing for disintegration is one of the most important issues in the enrichment of both minerals and processing of man-made raw materials. The solution of this problem is possible only through the creation of a fundamentally new highly efficient technique and technology for processing raw materials [1, 2]. It seems that the greatest prospects in this respect are the vibration methods of disintegration, in particular, the vibratory cone crusher based on a two-mass system without rigid kinematic connections between the crushing bodies, with vertical vibrations of the working bodies. In this machine, the principle of rational material destruction is realized – crushing without re-grinding [3-5]."

Jan 1, 2018

By Stephen Gay, Dewetia Latti

"When improving a plant a mineral processing engineer would like to know the mineral composition distribution. In order to assess this distribution in particles, as compared to the corresponding distribution in particle sections, a procedure needs to be applied to the observed particle sections. Such a procedure is called a stereological correction. There exists many stereological correction procedures, but one group of such procedures is based on using those stereological equations that do not require making assumptions regarding particle shape or texture.In particular Davy derived an equation to estimate the covariance of mineral composition distributions for particles from both particle sections and linear intercepts. Furthermore, this covariance can also be used to measure the variance of the composition distribution of each mineral.This paper shall present results verifying this equation. The experimental method was based on obtaining particle information from serially-sectioned particles. Particle samples selected for serial sectioning displayed a range of natural textures including liberated, binary and composite particles. The exposed surface of the polished sections were analysed using QEM*SEM. This procedure was repeated until all of the grains have been polished away. The covariance of mineral distributions were calculated from the serial sections and compared with that calculated using Davy’s equation."

Jan 1, 2003

By Gülay Bulut, Ünzile Yenial

"Water composition has a significant effect on flotation. A better understand the role of water composition in flotation is very important for process quality and performance. Based on source of process water, the concentrations of the dissolved ions, hardness, contaminants and residual composition of reagents can varied in the process water. The various water resources employed during lead and zinc flotation caused activation, depression or selectivity effects on minerals due to the presence of different ions in solution. Metal ions in these water resources were adsorbed on the ore, whilst ions associated with gangue minerals were released into the flotation pulp.This paper includes a research for the effect of different water compositions on lead and zinc sulphide flotation. Experiments were carried out five types of water such as tap water, recycling water, tailing dam water, underground mine water and sea water. The ore sample was obtained from Esan Balikesir-Balya mine. The mineralogical study of ore sample shows that it contains mainly galena, sphalerite, pyrite, hematite, quartz, diopside, epidote, calcite, and chlorite. It is found that recycling water and tailing dam water has a positive effect on recovery of lead and zinc minerals and detrimental effect on content of both minerals. This result may explain with remaining reagents in these waters. Underground mine water and tap water gave nearly the same recoveries of zinc. Sea water affects the recovery lead and zinc negatively."

Jan 1, 2014

By Crasta Jeason, T. Sreenivas, M. Narasimha

The subtle nature of the flow inside the hydrocyclone has encouraged development of mathematical models for predicting its performance, which are widely used in simulation of comminution circuits. But most of the models available are based on single average feed density. But the feed to hydrocyclone classifier is generally mixture of particles of different densities. This effect of varying density of feed particles on performance of hydrocyclone has been reported in literature. Further investigation of the effect of multi component feed on the performance of hydrocyclone is the objective of this work. This work involves experimental work to study multicomponent behaviour in various size cyclones. The performance of hydrocyclone for feed mixture of magnetite and quartz has been studied. The effect of presence of magnetite, a high density material on efficiency of separation of quartz has been analysed. It was observed that the effect of component interaction increases with feed solids concentration leading to an increased cut-size for a given optimum cyclone conditions. Based on the multi-component exiperiments available in literature, a concept for modeling the performance of hydrocyclones is proposed. A set of semi-empirical model equations for cut-size, sharpness of separation are presented. An attempt to validate the new hydrocyclone model on multi-component behaviour is made.

Jan 1, 2014

By V. Panayotov

Flotation practice usually uses the Sheridan-Grizvold selection method, where zinc minerals are activated by addition of copper sulphate and depressed by addition of sodium cyanide, ferrous sulphate, zinc sulphate or various mixtures of these reagents. The method is suitable for the flotation of sulphide ores, which, do not bear precious metals, such as silver and gold. When classical technology with cyanide is applied to depress zinc minerals, the precious metals, which are contained mainly into lead minerals, are dissolved into the solution, which represents a technological loss. In order to avoid this process, we have made use from the knowledge on the semiconducting properties of lead and zinc sulphide minerals. We have changed the surface charge of minerals by means of an electrochemical impact realized by direct current application and specially designed set of insoluble or semi-soluble electrodes. Thus, flotation separation of lead and zinc sulphide minerals was achieved, at increased recovery of lead, zinc and silver. The technology proposed was implemented in a Bulgarian flotation factory; it worked over 5 years providing significant, positive economic, technological and environmental impact. Silver recovery was increased by 0.8-1.0 %, and lead and zinc recovery was increased by 0.8-1.0 %. The technology is easily controllable and adaptable to raw materials and parameters of the technological process. It can be paid back for 6-8 months after the implementation. Keywords: lead-zinc flotation separation, electrochemical impact

Sep 1, 2012

By M. R. Robben

Carbonates have gained significant economic importance for the human kind. On one hand over a hundred uses are listed for carbonates. On the other hand, carbonates host base metal deposits. Although the carbonates play a significant part in the development of those deposits, in the mineral processing they consume acid and cause selectivity problems during flotation and leaching. Carbonates also accompany other industrial minerals as waste rock. For all those cases it necessary to find a technique to separate carbonate as early as possible in the processing chain. In this paper, the applicability of near-infrared spectroscopy (NIRS) sorting for the separation of carbonates is discussed. NIRS sorting is a sensor-based sorting technique, in which particles are singularly detected by a sensor and then rejected by an amplified mechanical, hydraulic or pneumatic process. This technique can for example be implemented in the process as a pre-concentration step for coarse particle sizes up to 300 mm. NIRS sorting discriminates among materials based on the difference that exist between their spectral properties in the near-infrared (NIR). Vibrations of molecular bonds in carbonates cause characteristic spectral properties in the NIR, which makes carbonates detectable, possible to identify, distinguish and separate from other rock materials. The spectral properties can also be used to distinguish between different carbonate minerals and mixtures. If the spectral variations are large enough for detection, sorting based on NIRS is possible. Feasibility studies on sensor-based separation of carbonates in the processing of talc, borate, fluorite, marble, zinc-oxides, copper sulphide and iron ore as well as the discrimination of calcite and dolomite mixtures are conducted and indicate the high potential of NIRS sorting in the minerals industry. Keywords: carbonate separation, sensor-based sorting, near infrared spectroscopy, NIRS sorting

Sep 1, 2012

By A. Morrison, P. Brito-Parada

"The separation of valuable and gangue minerals according to their surface hydrophobicity in a froth flotation tank occurs in both its pulp and froth phases. In the pulp phase, hydrophobic particles must be brought into contact with rising bubbles introduced at or near the bottom of the tank. In a mechanical froth flotation tank, this is primarily achieved through the agitation of the pulp by an impeller or by a rotor-stator system. However, the turbulent and mixing effects of such an impeller or rotor-stator system, necessary to promote bubble-particle interactions in the pulp, are not confined to the pulp zone, but are transmitted into the froth zone at the pulp-froth interface. This impeller-induced turbulence at the pulp-froth interface is compounded by the impulse of buoyant bubbles entering the base of the froth phase, reducing the stability, and thus separation performance, of the resulting froth. Hence, turbulence improves separation performance if it occurs deep in the pulp phase, but diminishes it if it occurs close to the pulp-froth interface. For this work, a performance-enhancing pulp phase insert was designed to isolate the impeller-induced turbulence from the pulp-froth interface in a laboratory-scale, continuously-operated froth flotation tank. The result was a shifted grade-recovery curve that allows the insert to be designed to maximize the recovery from the system without sacrificing the grade of the concentrate, or vice versa, along a spectrum of improved performance. This paper will present the insert design and development process that resulted in this improved grade-recovery curve, as well as a set of heuristics that could be used to design a similar insert for pilotand industrial-scale validation and deployment.INTRODUCTIONAn almost ubiquitous design feature of commercial flotation tanks is the enclosure of the impeller to create a concentrated turbulent zone (Mavros, 1992). These turbulent zone enclosures are varied-- from the rotor-stator design of, for instance, Outotec cells, to the air disperser design of Wemco cells-- but all share the same rationale: that turbulence is desirable to promote bubble-particle interactions (Ralston, 1999), and to produce smaller bubbles (Wills, 2006), but also undesirable because it promotes the detachment of valuable mineral particles from bubbles, and exacerbates entrainment-inducing mixing at the pulp-froth interface (Jameson, 2010)."

Jan 1, 2018

By Cagri Emer

In conventional mechanical flotation cells, when the size of particles exceed a particular value, that is of the order of 100 µm for metal sulphides, the recovery of particles decline rapidly. It appears that the turbulence in the agitated vessel is sufficiently intense to rupture the forces of attraction between the particles and the bubbles, so the large particles are flung off the bubbles in the turbulent field. It has recently been suggested, that a fluidized bed would be a very favorable environment in which to contact bubbles and the particles. In a fluidized bed, particles are supported by rising flow of fluid, which separates them from each other and allows them to move freely while remaining close together. In this novel method, bubbles injected into the fluidized bed are able to rise through it, colliding with hydrophobic particles, transporting them to the top of the column where they can form a froth layer that overflows into a launder. The flow in a fluidized bed is generally slow and nonturbulent, and preliminary experiments have shown, that it is possible to collect mineral particles as large as 1 mm and coal particles as large as 5.5 mm. If the upper particle size limit can be extended, there could be significant reductions in the overall energy consumption in concentrators. Calculations show for example that if the top size for flotation could be increased from 100 µm to 400 µm, there would be a reduction in grinding energy of the order of 40%. It is therefore, important to study the mechanism of coarse particle capture in fluidized beds. In this work, the factors governing the capture rate of particles, particularly the particle and bubble size, the fluidization velocity and the superficial gas velocity have been investigated, and the results will be presented.

Sep 1, 2012

By T. Fujita

A high-grade fluorite ore is converted into hydrogen fluoride to produce many kinds of materials containing fluorine. Recently, it is becoming necessary to use low-grade fluorite ore due to the depletion of high grade ore. The low-grade fluorites usually have impurities such as SiO2, P, CaCO3 and arsenic. The most impurities such as SiO2, CaCO3 and P can be removed by using flotation method. However, the removal of arsenic is difficult, and the arsenic contamination decreases the hydrogen fluoride production percentage. The novel technologies for processing low-grade fluorite ore are urgently needed, in order to lower the arsenic concentration to less than 100 mg/kg. In this study, the removal of arsenic from low-grade fluorite ore has been investigated by means of an autogenous grinding using tower mill in sulfuric acid aqueous solution and 0.3 mm zirconia balls in water. The nano grinding in water can prevent the dissolution of 0.3 mm size zirconia balls as grinding media by sulfuric acid solution. Experimental results showed that the arsenic concentration was reduced from 260 mg/kg to 90 mg/kg and CaF2 recovery reached 90% by this process.

Sep 1, 2012

By Jun Qiu, Ping Chen, Xianjun Lu

Nitrogen of different forms from wastewater was adsorbed by the natural bentonite and modified bentonite. The effects of adsorption conditions on the nitrogen removal were investigated. The experiment results showed that natural bentonite could easily adsorb ammonia while poorly adsorb nitrate, the organic bentonite modified by octadecyl trimethyl ammonium could effectively adsorb nitrate with the removal ratio increased from no more than 5% to 89%. Two kinds of bentonite were added together to the simulated wastewater which contained ammonia nitrogen of 15mg/L and nitrate nitrogen of 10mg/L, the dosages were 1.0g respectively. Both ammonia and nitrate had significantly decreased on conditions that the oscillation time was 1.0h and room temperature 20?. The optimum pH value for ammonia removal was 7 while for nitrate removal was above 7. The adsorption isotherm fitting results indicated that the Freundlich adsorption isotherm was the better model to describe ammonia adsorbed on the natural bentonite and the saturated adsorption capacity was 10.25mg/L, while the Langmuir isotherm could better describe the adsorption of nitrate on the organic bentonite and the saturated adsorption capacity was 14.35mg/L. Fully considering the interaction between different ions and controlling the appropriate conditions, removing nitrogen from wastewater by adsorption of bentonite is an economic and effective method.

Jan 1, 2014