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By Ajay K. Jha1

Drilling and Blasting are two important unit operations in the production cycle of a mine and a strong link exists between these two and other unit operations/subsystems like loading, transportation, and crushing. Under the present concept of ? Mine to Mill?, it is important to optimize the drilling and blasting operations by applying scientific approach to drilling and blasting using sophisticated instruments and new technologies, which depends heavily on Information technology (IT) to meet this imperative. Development of innovative models and software has lead to blast optimization process. Till date, the blast results are evaluated in terms of available empirical approaches like powder factor, which are too simple to exclude some key parameters or lack in providing reliability because of non-availability of user friendly IT enabled techniques. Although with the help of developed approaches, formulation of user-friendly software to assist the site engineers in effective post blast assessment has started but there is a dearth of holistic approach to design an optimum blast considering the techno-economic feasibility of the subsystems and the geo-mining conditions to achieve blast optimization. The science of IT enablement in drilling and blasting is capable to build innovative models for achieving blast performances which will be doped with productivity, economy and safety with due regard to environment. The present paper discusses the use of existing IT enablement in various mines of India citing the Indian scenario and the future requirements for achieving the techno-economics in overall mining operations.

Sep 1, 2012

By M. Tang

The phosphate ore sample was taken from the iron tailings after recovering most of magnetite by magnetic separation in Longlin, Yunnan Province of China. Batch flotation tests had been conducted to upgrade the phosphate concentrate by conventional fatty acids reagents under 70% -75 µm of the particle size; however, the unsatisfied results (P2O5 grade of 27.84% and recovery of 49.25%) were obtained. Also there are a large amount of slimes trapped in the concentrate and high-dosages consumption of reagents, for example, more than15 kg/t soda ash and 2 kg/t sodium silicate at only one-staged roughing. Based on the analysis of X-ray diffraction (XRD) for the sample, most of gangues are clay, quartz, and chlorite, which may easy to over-grind and deteriorate the flotation process either on reagents consumption or slurry fluidity or viscosity. A hydro-cyclone had been introduced to pre-concentrate the phosphate ore by scrubbing the slime before flotation, which can result obviously in reducing the dosages of soda ash from 15 Kg/t to 4 Kg/t, and raising the grade of P2O5 in the concentrate from 27.84% to 36.13% at the expense of about 4% recovery of P2O5. They also substantially reduced the time of sedimentation of concentrate after flotation from ~10 to ~1 min. In this paper, the effects on the recovery of P2O5 by the different dosages of flotation reagents with or without de-sliming were studied, with the objective of determining the different effects on the functions of flotation reagents by slime during flotation. Keywords: de-sliming, phosphate, soda ash, flotation

Sep 1, 2012

By D. I. Verrelli

Within the flotation community a belief has developed that some particle shapes are more ?floatable? than others. This is usually attributed to an influence of particle shape or roughness on the induction period required to achieve attachment between the particles and the air bubbles in the pulp. Up to now, such measurements have not been able to readily isolate the effect on individual flotation subprocesses. In contrast, our experimental apparatus, the CSIRO Milli-Timer, enables us to directly observe the process of particle?bubble interaction and attachment by means of a high-speed video recording, thus providing a direct measure of the induction period for attachment. To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles ? spheres and angular ?frit? ? in a range of tightly-sized fractions. In doing this, we take care to account for the influence of other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity. These parameters are recorded as variables for each interaction, and corrected for using multiple nonlinear regression. Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. Particle shape in mineral processing is a consequence chiefly of the mineral type and the type of grinding employed. The results presented herein indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size. Keywords: attachment, bubbles, flotation, induction period, particles, shape effects, surface roughness

Sep 1, 2012

Opportunities to monitor and control primary grinding mill performance are strongly sought after in the mineral processing industry. Currently, limited on-line information about mill charge motion and content is available to mill operations for control purposes, leading to periods of lower throughput, instability, variable product size and accelerated mill liner and lifter wear. In response to this need, CSIRO has developed an on-line surface vibration monitor for primary grinding mills which produces data that has been shown to provide new information about the mill charge in terms of toe and shoulder position, as well as potentially key features such as the overall charge level, the distribution between rock and balls in the mill, and the impact of the charge on the mill liners and lifters. This paper outlines the key features of the on-line monitor system, particularly those relating to data transmission, data analysis, and the design of the monitor and its independent power supply. It describes the coupling of single vibration sensor data from the CSIRO on-line monitor to the actual operating conditions of a SAG mill and how the vibration response and hence mill operating conditions vary as a function of time, including during mill equipment failures such as a broken discharge grate. Opportunities for improved mill control based on the data from the on-line monitor are also discussed, as well as the implications in terms of mill processing and maintenance performance. Recently a CSIRO monitor was also installed on a ROM ball mill and analysis of the vibration sensor data from this installation is currently underway. Preliminary findings from this installation will be presented along with comparisons of generic information, such as toe position (measurement precision and operation variability) and vibration signal (intensity, sensitivity and operation variability), between this type of primary grinding mill and AG/SAG mills.

Sep 1, 2012

To extract the gold from refractory gold concentrate with high sulfur and arsenic, the gold concentrate was catalytically oxidized to expose the gold for cyanide leaching. The effects of reaction temperature, initial nitric acid concentration, reaction time and initial gold concentrate concentration on the conversion rate were studied. The results show that the appropriate conditions for the catalytical oxidation of this gold concentrate are: reaction temperature of 65 oC; initial nitric acid concentration of 25% (wt.); reaction time of 1.5 hours; initial gold concentrate concentration of 10% (wt.). Under such conditions, the conversion rate of gold concentrate is 92%. The solution can be used to prepare nano-iron oxide red pigment. Gases released in the process can be recycled and reused by oxidation absorption. A chemical background of catalytic oxidation is proposed.

Jan 1, 2014

In looking to the future of mineral processing the focus is typically on improved processing units. Basically it is a search for an elusive wonder machine that could revolutionise the economy of mining: the sorter that strips 50% of the ore with only a few % loss of value; the comminution device that uses 5% of the energy while producing fully liberated particles; or the recovery device capable of producing a 99% recovery at 99% grade. These aspirations are propounded against a reality backdrop of sorters rusting in back yards, mill throughputs below design and varying by 30%, cyclones flaring and cut-sizes fluctuating, mediocre recoveries and soaring processing costs. This disconnect between aspiration and reality appears, to these authors at least, to be a mighty chasm. Moreover, it remains one over which we are expected to magically leap rather than methodically bridge. Indeed one may be forgiven for thinking that should such a wonder machine come along, taking advantage of it would be highly improbable. Questions would inevitably emerge on how to feed the correct material, how to cope with the wide variability of feeds, how to control such advanced equipment and how to handle the new product from such a machine. It is likely these questions might lie unanswered, or more regrettably, unasked. It is generally accepted that as an industry we are exceedingly unlikely to teleport from the current status quo to an entirely new reality in a single flash. It is our thesis that the probability of these magical machines materialising is remote, and even if they miraculously appeared, we simply wouldn?t know what to do with them. Rather, it is our contention, that a step change will only arise through a staircase rather than from a single giant leap. We should focus on building those steps and linking them together into a firm structure ? a workable mineral processing circuit. This paper addresses the alternative of a coherent set of modest but significant improvements, integrated to produce the step change we desire: essentially, a reduction of processing energy to below 40%, which we believe is achievable without recourse to any mystical machines. A key underlying capability to designing these dramatically improved processes, is the weaving of independent process models into a coherent circuit simulation, in order to design the new generation of mineral processing circuits. Keywords: step change, circuit design, circuit simulation, energy reduction

Sep 1, 2012

By Sushanta Majumder

The physico-chemical characteristics of raw materials used for the production of iron ore pellets have a strong influence on the productivity of pelletization operations and on the quality of pellets. Since iron ores from different sources are used for making iron ore pellets and since the quality of the ores varies with time, there is a need to optimize and control pellet plant operations on a regular basis to achieve optimum productivity while maintaining pellet quality within the desirable specifications. In order to achieve this objective, a model-based on-line optimization system was implemented on two industrial scale induration furnaces. The optimization system consists of a rigorous mathematical model of the induration process, a model for the permeability of the bed of pellets, a statistical model for the quality of iron ore pellets and an optimization module based on sequential quadratic programming. The rigorous model is tested on-line using the wind-box temperature available real-time. The process was optimized to enhance induration furnace productivity for the given constraints on pellet quality parameters such as the cold compressive strength (CCS) and Tumble Index (TI), and other equipment design parameters. Process variables such as induration machine speed, cold air flow rate and hood temperature profile were used as the optimization variables. The on-line optimization system was successfully implemented in two industrial induration furnaces and lead to enhanced productivity. Details of the on-line optimization system and results of process optimization will be presented.

Sep 1, 2012

By S. M. H. Haddad, M. Saghaeian, R. Hejazi

"Due to limited water resources in mineral processing plants, increasing the efficiency of iron tailing dewatering system in order to obtain more usable water is very important. In this research, flocculation process, as one of the best method for water recovery, was investigated by using one organic cationic and three anionic types of flocculants with different dosages (10, 20, 30 g/ton) and iron ore tailing slurry (8 % w/w solidity) in series of graduated cylinders and obtained results were compared. it is observed that for tailing sample, the anionic flocculants have a significant effect on the settling rate of solid particles compared to the cationic types. Furthermore, effects of temperature (10, 23 and 43 ºC) and pH (2, 7 and 12) on the rate of settlement and turbidity was studied by utilizing the best flocculant. Findings showed that by increasing the amount of flocculant dosage, sedimentation rate went up and turbidity decreased. Comparison the out-put data of tests indicated that at temperature 23 °C and pH=7, the best results for both of faster settling rate and producing more clear water were reached. It should be considered that lower temperature has a more negative effect on the sedimentation rate and overflow water quality. So it will be predicted that for cold seasons, the consumption of the flocculant powder would be higher than the moderate or warm seasons. Also, coagulation/flocculation was evaluated by applying organic cationic coagulant added to anionic flocculant in three different times. Different ratios of coagulant to flocculant was examined (70%:30%, 50%:50%, 30%:70%) as well. Overall, utilizing coagulant had desirable influence on sedimentation experiments and obtaining high quality water. 1- INTRODUCTION In mineral Factories, among the important processes, solid-liquid separation process due to limited resources of water is very important and operates on iron ore tailing in settling tank as thickener in order to gain clear water for preventing water loss and applying again in plant units (Ciftci and Serhat Isik, 2017). Iron ore tailing include inharmonious compounds of iron oxides, silicates and aluminum-silicates. The percentage of solid in the tailing usually changes between 5 and 10 percent (Dash et al., 2011). One of the major problem about dewatering of tailing in thickener is solid-liquid separation of slurries with high stability because of fine particles. It means that rate of sedimentation is very slow and recovered water quality is inappropriate. This issue can be solved to a large extent by factors such as pH control, ionic strength and flocculation/coagulation process which results in aggregation of particles so that settlement by gravity is happened (Dash et al., 2011)."

Jan 1, 2018

By M. Rudolph, D. H. Hoang, N. Kupka

"Froth flotation has been subjected to modelling since the 1930s and there is a large variety of approaches that intend to portray the entire process. Among these, three fundamental models could be considered exhaustive: the Pyke model [1], the Yoon model [2] and the Schwarz and Koh model [3]. The first model makes use of the generalized Sutherland equation collision model, the Dobby-Finch attachment model and its own stability model, the second model considers an extended DLVO approach for the attachment and stability whereas the third model makes use of computational fluid dynamics. Using a scheelite ore as a test case, a specific batch flotation test was repeated ten times and analyzed for chemical assays, mineralogical studies and froth properties. The detailed data are used to feed the three flotation models aforementioned in order to compare the outcomes of the three approaches, their capacity to reflect reality and to predict it. This article intends to pave the path towards reliable process models incorporating in depth mineralogy information, e.g. surface liberation, particle size and particle shape. KEYWORDS Froth flotation fundamental models, scheelite, automated mineralogy, critical assessment. INTRODUCTION In mineral processing, only three approaches aiming at describing froth flotation fundamentally could be considered exhaustive: Pyke’s collision and sliding approach [1], Yoon’s kinetic approach [2] and Schwarz and Koh’s approach [3]. The models will hereafter be referred to as Pyke model, Yoon model and Schwarz and Koh model. The first model makes use of the generalized Sutherland equation collision model, the Dobby-Finch attachment model and its own stability model, the second model considers an extended DLVO approach for the attachment and stability whereas the third model makes use of computational fluid dynamics. All three approaches rely on the widely accepted idea that flotation is a kinetic reaction dependent on a flotation rate constant kp, as expressed in Eq. [4]:"

Jan 1, 2018

By F. Y. Kang

Graphite with layers structure is easily to form graphite intercalation compounds (GICs) by means of intercalation reactions due to the weak cohesion force among carbon layers, van der Waal?s interactions. By controlling the oxidation-intercalation, high quality exfoliated graphite with low residual sulfur content and MClx-GICs (M=Fe, Co, Ni, Cu, Zn) powder for electromagnetic wave absorbing and shielding materials have been invented. The expansion volume of expandable graphite can be larger than 160 mL/g while the residual sulfur content is less than 800 ppm. The MClx-GICs powder can shield infrared ray and laser completely up to 15 min. We have also in-vented exfoliated graphite for heavy oil adsorption and mild-expansion exfoliated graphite for anode materials in lithium ion battery by controlling the intercalation/de-intercalation. The exfoliated graphite can adsorb heavy oil up to 80 g/g, it also exhibits better performance than commercial active carbon in sewage treatment. The mild-expansion exfoliated graphite as anode material shows high capacity of 370 mAh/g and good cycle performance.

Jan 1, 2014

By Z. K. Liu

Production of the amines collectors and cation surfactant gives out the liquid waste containing high COD (Chemical Oxygen Demand) and ammonium & nitrogen, which is difficult to be treated with conventional biological method to reach waste water discharge standard. In this paper an engineering practice of treatment on the liquid waste by the technology combined high effective microbe with A/O (Anaerobic& aerobic) process is presented. The quality of treated water comes up to class A national standard for discharging.

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 Yang Zhao, Tao Xiu-xiang, Chen Song-jiang

"China is rich in low-rank coals that account for 45.68% of existing coal reserves in China. The clean and efficient utilization of low rank coals is of great significance for ensuring the effective energy supply and promoting economic development and environmental protection. In order to solve the difficult problem in flotation of low rank coal, it has become the focus of research in the related field that oily bubbles instead of air bubbles are taken as a carrier in flotation to improve the attachment efficiency and recovery of low rank coal. In this paper, low rank coal slime collected from Shendong mining area was used as the experimental material, and it focused on the characteristics of oily-bubble flotation process of low rank coal. Additionally, difference in conventional flotation and oily-bubble flotation was discussed. The induction time between air bubbles, oily-bubbles and fine low rank coal particles was measured. The results indicated that the induction time between oily-bubbles and coal particles was obviously lower than that of air bubbles. By comparing the foam height of air and oily bubbles, it was found that the amount of oily bubbles is less than air bubbles, causing relative low flotation rate of oily-bubble flotation at initial stage. Besides, the maximum foam height and half-life of air bubbles and oily-bubbles were measured respectively. The results showed that the stability of oily-bubbles was higher than that of air bubbles, which is benefit for the enrichment of concentrates. The clean coal water recovery of oily-bubble flotation is lower than that of air bubble flotation, which indicated oily-bubble flotation is lower in water entrainment. INTRODUCTION China is the largest energy consumer in the world, accounting for 23% of global energy consumption in 2016 and 27% of global energy consumption growth. Whereas coal is taken as the major primary energy source and its share of China’s primary energy consumption is 62% in 2016, in which the low rank coals, such as lignite, long-flame coal, weakly caking coal, and non-caking coal, accounted for about 50% of total coal production capacity (China’s energy market in 2016, BP). Moreover, the exploitation and utilization of low rank coals and other coals that are difficult to float have been an important strategy for China’s sustainable development of the coal industry (Liu et al., 2014). However, the combustion of low-quality coals leads to a serious environmental pollution. In addition, the deterioration in geological conditions of coal resources, and the increasing improvement in the mechanization for mining significantly caused the increased amount of fine coal."

Jan 1, 2018

By Xinyang Xu, Chen Zhang, Lixia Li, Zhitao Yuan

"Density functional theory was employed to clarify the mechanisms of the activation of a quartz surface and its collection by the flotation method at the molecular level. The calculation results indicated that hydrogen bonds on the quartz surface (1 0 1) existed in pairs while in contact with water. The simulation was carried out to investigate the different effects of Ca2+ and Ca(OH)+ on a quartz surface with hydrogen bonds, and the results suggested that Ca(OH)+ most likely adsorbed onto and activated the quartz surface. Mulliken population analysis of the external oxygen atom of the quartz surface, calcium atom of Ca(OH)+, and the oxygen atom of oleate showed that there were electron transfer and the formation of a chemical bond between Ca1-O1 and Ca1-O3, which were indicative of strong interactions between the three atoms. In addition, the –OH of the Ca(OH)+ contributed to the activation, which suggested that the Ca(OH)+ group acted as a bridge between the surfaces of oleate and quartz.INTRODUCTIONFlotation is an effective separation method in mineral processing that takes advantage of the physicochemical differences between minerals and gangue, and the properties of the mineral surfaces play a key role in this process (Liu et al. 2016, Qin et al. 2017). In the reverse flotation process of iron ore, gangues are captured by cationic or anionic collectors and floated with air-bubbles as tailings, and the pre-depressed iron oxide minerals are left at the bottom as concentrates (Lima et al. 2013, Yianatos et al. 2015, Zhu et al. 2015). Quartz (SiO2) is one of the major gangues of hematite ores and cannot be easily removed. It is a naturally hydrophilic mineral, in which silicon is the cation in its crystal structure and has very limited solubility. Therefore, quartz must be activated, usually by metal ions, for its effective rejection as a float-product by reverse flotation (AIME. et al. 1976)."

Jan 1, 2018

By S. Groudev

Acid drainage waters generated in the uranium deposit Curilo, Bulgaria, were treated by means of a pilot-scale passive system consisting of a permeable reactive multibarrier and a constructed wetland connected in a series. The multibarrier had a total volume of 23 m3 and consisted of an alkalizing limestone drain and an anoxic section for microbial dissimilatory sulphate reduction, bio-sorption and additional chemical neutralization. The waters had a pH in the range of about 2.5 ~ 4.0 and contained radionuclides (uranium, radium), heavy metals (copper, zinc, cadmium, lead, nickel, cobalt, iron, manganese), arsenic and sulphates in concentrations usually much higher than the relevant permissible levels for waters intended for use in agriculture and/or industry. The water flow rate through the multibarrier varied in the range of about 1 ~ 17 m3/24 h, reflecting water residence times of about 300 ~ 18 hours. An efficient removal of pollutants was achieved by the multibarrier during different climatic seasons, even during cold winter days at external air and water temperatures close to 0oC. The multibarrier effluents were enriched in dissolved organic compounds and in some cases still contained manganese and iron in concentrations higher than the relevant permissible levels. These pollutants were removed in the constructed wetland as a result of the activity of different heterotrophic microorganisms, including some bacteria able to oxidize the bivalent manganese and iron ions to Mn4+ and Fe3+, respectively.

Jan 1, 2014

By Ranjeet K. Singh

Kelsey Centrifugal Jig was found to be promising for the beneficiation of fine coal particles. The present study was aimed at in-depth understanding of the separation features of Kelsey Jig through detailed experimentation. Beneficiation of fine coal of size 150 x 300 µm was studied in a laboratory Kelsey Jig. The thickness of the ragging bed is found to be an extremely crucial parameter apart from the other process parameters such as rotational speed and pulsation frequency. A constant pulp density (25% solids) of the feed slurry was maintained in the study. The feed rate was also kept constant at 50 kg/hr dry solids. Silica sand of size -1.68+0.85 mm was used as ragging material to avoid the pegging of internal screen having an opening of 425 µm. The rotational speed was found to have significant effect on the depth of the ragging bed and its porosity, which influenced the separation performance considerably. Pulsation was identified as the key factor in stratifying the coal bed and defining the misplacement as well as ragging bed porosity, which influenced the mass yield and quality of the products. Beneficiation studies were carried out with rotational speed varying between 900-1000 rpm while pulsation frequency was kept within 850-925 rpm. In a single pass through the Kelsey Jig 7-8% (absolute) reduction in the ash content of the feed material was observed at more than 55% mass yield. High rotational speed, moderate pulsation, and low ragging bed depth favored good cleaning. A high bed depth was found to facilitate rejection of high ash materials. It was established that Kelsey Jig is effective in fine coal cleaning though a controlled operation is required in order to achieve superior performance. Keywords: enhanced gravity separator, g-force, separation performance, ragging material, coal beneficiation

Sep 1, 2012

By Carina Ulsen

The existing construction and demolition (C and D) waste recycling technologies and standards have been essentially focused on the production and use of coarse recycled aggregates. Very few papers focus on the production of recycled sand, although some previous results show that fine aggregates fraction represents around 40 to 60% (in mass) of the Brazilian waste and it is usually used as road sub-base or disposed in landfills. The quality of the recycled aggregate is strictly related to the content of porous and low strength phases, mainly the patches of cement remaining on recycled aggregate surface. Some technologies have already been described in the literature, even though, to the moment none of these technologies has clearly succeeded in reaching the large market available. This paper presents a summary of the main properties of the sand produced from C and D waste by tertiary crushing at vertical shaft impact crusher (VSI). Additionally mineral processing technologies were applied on the attained product, such as gravity concentration by shaking table and spirals and removal of cement paste by attrition. The main properties of recycled sand are discussed and compared to the previous C and D waste, respectively: particle size distribution, particle shape, chemical composition, cement paste content and porosity. The results demonstrates that the crushing allowed producing a VSI-sand with low porosity and water absorption due to the increasing on the content of silicates from natural rock phases and increasing liberation between these phases and porous cement paste; the particles from the attained product presented also a better shape (sphericity and aspect ratio). The attrition tests assayed on VSI recycled fine aggregates accomplished a further selective disaggregation of cement paste and other porous materials - the porosity was reduced from 10% to 7%. The concentration by shaking table at narrow sieve fractions led to a product with low porosity and reduced content of cement paste, however, concentration on spirals did not succeed since separation was performed essentially by the size of the particles. The heavy product from shaking table represented almost 75% in weight and has less than 60% recovery of CaO+LOI, and expressive reduction on porosity. The aim of producing sand from construction and demolition waste through mineral processing unit operations changes the recycling approach and contributes for up cycling the recycled sand. The exhaustion of sand deposits on Brazilian large centers, the increasing price and the construction boom encourages the development of alternative materials as construction raw material. Keywords: recycled sand, construction and demolition waste, technological characterization

Sep 1, 2012

By B. McFadzean

Thiol collector mixtures are commonly used in the flotation of base metal sulfides and platinum-bearing ores. There are synergistic benefits claimed for these collector mixtures, with mixtures lowering total dosage requirements, improving coarse particle recovery and the rate of flotation. Some of the secondary collectors are known to have frothing effects. Therefore, a previous study aimed to decouple froth and pulp effects and considered only the bubble-particle attachments in the pulp. This was achieved through microflotation experiments, where various ratios of the ethyl and isobutyl chain lengths of xanthates, dithiocarbamates and dithiophosphates were used as collectors. Results from these experiments showed a marked increase in galena recovery using mixtures of xanthate with either dithiophosphate or dithiocarbamate. In the current study, the froth phase was introduced in the form of batch flotation studies to determine whether benefits noted during microflotation experiments would be carried through to a more realistic froth flotation scenario. The findings show that there was no significant difference in the flotation recovery between the best single collectors and mixtures of these collectors. In addition, single collectors that behaved poorly in microflotation experiments showed good flotation performance in the batch flotation experiments. The differences between the microflotation results and the batch flotation results are attributed to differences in particle froth stabilizing properties and/or differences in energy input between the microflotation and batch flotation cells. In addition, galena and pyrite showed marked differences in frothing effects and in their preferences for collector type. Keywords: froth flotation, collector mixtures, sulphide minerals

Sep 1, 2012

By V. K. Chandaliya

N-Methyl-2-pyrollidone (NMP) has already been proven a good solvent for extraction of coal. It is believed that organic components of coal are likely to be dissolved with the solvolytic power of NMP. During dissolution process, original coal also gets disintegrated and thus helps in further extraction. Coal extraction highly depends on temperature, coal to solvent ratio, N-Methyl-2-pyrollidone (NMP) to Ethylenediamine (EDA) ratio and the size of coal particles. The process has been established in the laboratory. There is no reference available beyond lab scale. In present study, we are running a bench scale plant with 40 kg/batch capacity. Design of experiment was done in such a way that the optimum zone of the process gets evaluated for clean coal having low ash with high yield. Bench scale plant trial was conducted based on optimum zone developed during design of experiments (DOE). From the DOE analysis it was observed that feed size and coal to solvent ratio are important parameters for this process. Total 27 experiments (four factors with 3 level of variation) were designed through Box-Behnken model. It was observed that -0.5 mm feed size of coal, 150 °C extraction temperature, 17:1 NMP to EDA ratio, 1:9 coal to solvent ratio was optimum conditions. The results obtained at optimum conditions are 50% clean coal yield with 5% ash.

Sep 1, 2012

By Masakazu Niinae, Tasuma Suzuki, Mai Moribe, Yohhei Okabe

Bench-scale electrokinetic experiments were performed to elucidate the electrokinetic remediation mechanisms of arsenate from artificially contaminated kaolinite. The electrokinetic experiments in which a constant voltage was applied demonstrated that high soil pH favored arsenate remediation with respect to both the remediation time and electricity consumption. It was also demonstrated that applying a pulse voltage (1 hour ON, 1 hour OFF) significantly improved the electricity consumption efficiency when the soil pH was maintained at the initial value during the experiments; this trend was not observed when the soil pH was gradually increased from the cathode side. These electrokinetic experimental results indicate that the remediation rate-limiting step varied with soil pH. When the soil pH was maintained at the initial value of 7.2 during the experiments, arsenate desorption was the remediation rate-limiting step rather than the migration of dissolved arsenate toward the anode. Conversely, when the cathode pH was not controlled and the soil pH was correspondingly increased gradually from the cathode side, the migration of hydroxyl and desorbed arsenate ions toward the anode played a more important role in the control of the overall remediation efficiency.

Jan 1, 2014