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By F. S. Thurner

This paper, a description of the new ore-unloading and stockpiling facilities at the Sydney Works of DOSCO Steel Limited, deals with a new approach to arrive at the most economical solution to combine ore unloading facilities for common bulk carriers and for different types of self-unloading vessels. Also discussed is the design and installation of a 1-mile-long steel-cord belt conveyor sys-tem with a most modern type of mobile belt conveyor stacker, along with automatic and semi-automatic controls for the entire ship-unloading and stockpiling operations.

Jan 1, 1968

By H. H. Claudet

PROBABLY the first flotation mill for treating molybdenite ores was put into operation .in Norway during 1913, when the writer was employed to introduce and apply the Elmore vacuum flotation process at a mine in southern Norway. These operations proved successful and led to other similar installations in that country. It remained, however, for Norwegian engineers themselves to iron out their difficulties and establish the molybdenum industry on a basis which ultimately attained world importance. Just as today, an urgent demand for molybdenum arose during the world war of 1914-18. By 1916, many molybdenite properties were in operation in Canada and several small concentrating mills were under construction. At one of these, in the Ottawa Valley district, the opportunity came for applying the Elmore vacuum flotation process, using a flow-sheet similar to that adopted in Norway. Later, as one of the staff of the General Engineering Company, who had already developed a highly efficient flowsheet for treating molybdenite ores, using the Callow pneumatic flotation process, the writer devoted considerable time to research work and investigations on a number of molybdenite projects and deposits in eastern Canada. The bulk of Canada's production of molybdenite was coming at that time from the Moss mine at Quyon, Que., where concentration of the ore was effected by water-film flotation. It is of interest to note that this process, based on the principle of surface tension, had been developed and introduced by the late Henry E. Wood, of Denver, Colorado- one of the original owners of the Moss mine-at the time he was investigating the Elmore vacuum process in his Denver plant. The process, with certain modifications, was used at several other properties in eastern Canada, and notably in the ore dressing laboratories of the Department of Mines at Ottawa and in a plant at Renfrew, Ont., in both of which ore from deposits in various parts of Canada was treated, with recovery of very appreciable amounts o much needed molybdenite. During the summer of 1917, the water-film flotation mill at the Moss mine was dismantled and the plant was re-modelled by the General Engineering Company to include the Callow system. This installation, using improved flotation methods, was highly successful both as to recovery and grade of concentrate, and proved a decided advance in molybdenite concentration, a recovery of upwards of 90 per cent being obtained, with a concentrate grading over 90 percent MoS2.

Jan 1, 1944

By S. Gheibi, H. S. B. Duzgun, N. Dadashzadeh

It is widely recognized that there are various uncertainties in the analysis of rock slope stability owing to inadequate information for site characterization and inherent variability and measurement errors in geological and corresponding parameters. Therefore, reliability-based approaches that allow the systematic and quantitative treatment of these uncertainties have become a topic of increasing interest in rock slope engineering. There has been extensive reliability analysis of rock slope stability in the literature. However, all of these analyses are based on the First-Order Reliability Method (FORM). The probability of failure of a rock slope in the First-Order Reliability Method is provided by a linear approximation of the failure function. The FORM is most commonly used because it is efficient; its accuracy, however, deteriorates when the nonlinearity of limit-state function increases. A better approximation of the failure function can establish a more accurate value of the probability of failure. The Second-Order Reliability Method (SORM) overcomes this drawback with a cost of lower efficiency in terms of the number of function calls and computation expenses. Despite considerable studies of the application of the SORM in other engineering fields, a few attempts have been made in the slope stability studies. In this study, a recently published Second-Order Reliability Method with First-Order Efficiency (SORM-FOE) is implemented on a selected rock slope in Amasya, Turkey. The SORM-FOE overcomes the low efficiency of the SORM by decreasing the number of function calls. The probability of failure of both FORM and SORM-FOE are obtained and the results are compared. It is shown that, in high value of failure probability, SORM’s do not significantly affect the analysis and design. However, in very low failure probability, the discrepancy between FORM and SORM-FOE becomes pronounced. It is also shown that, where the second order methods are required, the SORM-FOE is more efficient than the conventional curvature fitting methods in terms of computational costs.

Jan 1, 2015

By PETER O. SANDVIK

The Cargill deposit, located 32 km south west of Kapuskasing, Ontario, was discovered by International Minerals and Chemical Corporation in 1975 and has been evaluated through an extensive program of drilling, chemical analyses, metallurgical tests and engineering and economic studies. The Cargill alkalic complex, comprising mainly carbonatite and pyroxenite-amphibolite rocks, was intruded into the rift system of the Kapuskasing magnetic-gravity high. Weathering and leaching under assumed temperate to cool climatic conditions plus faulting, shearing and/ or initial petrographic variations within the carbonatite developed a small, locally confined karst system. This resulted in a thick enriched leached carbonatite zone capped by troughs and sinks, and filled with a residuum of apatite, goethite, clay and other minerals. Residuum thickness ranges from nonexistent on ridges to 170 m in troughs and sinks. Apatite values are 5 to 15% in fresh carbonatite, 20 to 40% in leached carbonatite and 20 to 98% in residuum. A tentative open-pit mine designed for preliminary feasibility studies is estimated to contain 62.5 million tonnes averaging 19.6% P20 5.

Jan 1, 1984

By D. Chadwick, J. W. Matousek

Between 1860 and 1890 -- from the time of the American Civil War to the last decade of the 19th Century -- nickel production in North America was dominated (even monopolized) by the output of the industrial complex of the Gap Nickel Mine near Lancaster, Pennsylvania and the American Nickel Works in Camden, New Jersey. In some years, from one sixth to one third of the world's metallic nickel supply came from this enterprise. Mining and smelting were conducted at Lancaster; a matte of high iron content was shipped to Camden for pyrometallurgical and hydrometallurgical refining to produce nickel metal, copper sulfate, and cobalt oxide. The high purity nickel product was rolled into sheet for marketing, primarily for coinage, as nickel had few other uses at that time. The undertaking experienced all of the problems that face the mining and metallurgical industries of today: declining reserves, high labor and fuel costs, high transportation costs, fluctuating demand and prices, pollution concerns, and foreign competition. The technical features of the geology; the mining, smelting, and refining operations; and some of the economic aspects are assessed. The view is taken from that of the present time -- seeking those lessons from history that we are supposed to learn or face the prospect of repeating the mistakes of the past.

Jan 1, 2005

By K. B. Han, S. Winkler, M. J. Benoit, M. J. Worswick

"Automotive heat exchangers are fabricated by forming multi-layered aluminum (Al) alloy brazing sheets into the desired geometry and subsequently passing the assembly through a furnace for brazing. As manufacturers seek to use thinner gauge and higher strength sheet to reduce vehicle weight, forming of the Al alloy sheets has become a challenge. Warm forming has previously proven to allay these forming concerns, but no consideration was given to the effect of increasing the forming temperature on brazing. Recently, it was shown that annealed sheet was more susceptible to the detrimental phenomenon of liquid film migration (LFM) during brazing if formed above 150°C, while work hardened sheets showed no increased susceptibility to LFM with increasing forming temperature, up to 250°C. In the current study, the brazing performance of simulated battery cooling plates was investigated. The plates were fabricated both from fully annealed and work hardened sheets. Brazing was assessed by microstructural evolution during a brazing cycle. The post-brazed microstructure varied with strain and forming temperature in plates made from annealed sheets, while no variation in microstructure with location or forming temperature was observed in plates formed from work hardened sheets.INTRODUCTION Since the 1970’s, one common method of fabricating automotive heat exchangers has been by forming multi-layered aluminum (Al) alloy sheets, and subsequently brazing the formed components together in a controlled atmosphere furnace. The Al alloy sheets used are comprised of at least two Al alloys roll bonded together, but can consist of additional layers, depending on the application; at minimum, the sheets are comprised of a core and clad layer. The core layer, often an AA3xxx alloy, remains solid throughout processing and provides strength to the assembly. The clad layer is always one of the AA4xxx series alloys which, due to their high silicon (Si) content, have a melting temperature range well below that of the core alloy. When the sheet is passed through the brazing furnace, the clad alloy melts to provide the brazed joint filler metal throughout the assembly, while the core alloy remains solid. In order to achieve cost and weight savings, heat exchanger fabricators have used Al alloy sheets with reduced thickness. However, deformation and brazing of these increasingly thin components remains a concern (Zhao & Woods, 2013). Furthermore, springback has been observed after forming sheets of higher initial strength (i.e. work hardened conditions), leading to flatness issues of formed components. Consequently, the ability to form high quality brazed joints is difficult in components formed from higher strength brazing sheets."

Jan 1, 2018

By R. Heikkilä

As a part of a large research and development program in Finland, a system calibration for an UAV measurement method having practical experiments in a Jorvas Railway Yard design and construction project. The Railway yard construction are was measured using an UAV measurement device by Smartplanes (Smartone) and using some reference points measured by a GNSS device. The measured data was cleaned, combined and adjusted through Least Squares Optimization using the software developed by a Finnish company Pieneering Oy. As references, two different laser scans as well as total station surveys were used. For applicability evaluation, the accuracy of measurement, the reliability of measurement, and the economy of measurement were used. Based on the comparisons, the achieved precision of the UAV measurement was high, instead the accuracy of measurement was not sufficient in this case. The principle of this photogrammetric measurement includes a lot of redundant observations making it possible to achieve a high level of reliability. The economy in this Railway Yard Design project was not able to achieve.

Aug 1, 2013

By Harold S. King

TWO summers ago I had the privilege of visiting No. 18 colliery at Glace Bay. Underground, we travelled along the haulage-way behind a powerful electric locomotive. The motor in this locomotive began to smoke badly and a carbon tetrachloride type of extinguisher was used several times during the trip. At the time, I noted a strong odour of phosgene. On my return to Sydney, I spoke to Mr. Harold Gordon, Assistant to the General Manager of the Dominion Steel and Coal Corporation, and warned him of the danger of using this type of fire extinguisher in confined spaces, since it is a well known chemical fact that phosgene, a dangerously toxic gas, is formed by the decomposition of carbon tetrachloride. This danger does not seem to be widely recognized, so it seems advisable that a more general warning be published. Attention was first drawn to the danger by the death of two men in the United States Navy Department subsequent to breathing fumes from carbon tetrachloride used in a fire, and when an employee of the Bureau of Mines also was overcome while fighting a fire with carbon tetrachloride liquid. These accidents led to an investigation of the decomposition products of carbon tetrachloride by a group of workers in the Research Laboratory of the Pittsburgh Experimental Station, U.S. Bureau of Mines, the results of which were published in the October, 1920, number of the Journal of the .Franklin Institute (1). Their experiments were conducted by two methods. The first consisted in applying the liquids to actual fires and -to hot metal in a closed room of 1,000 feet capacity, where the gaseous products, mixed with air, could be retained and analyzed. The second method was to pass the vapour:s in air through heated tubes of iron or quartz, where the humidity of the air and the temperature could be controlled.

Jan 1, 1939

By J. Xie

In underground coal mining, the potential for an outburst of coal and gas is considered to be one of the major hazards. As such, considerable emphasis is given to understanding and preventing such events. A number of indices are used in the prediction of the outburst in a coal mine. The main indices include initial gas desorption rate, gas pressure, gas content, coal strength, gas flowrate from a borehole drilled in a coal seam, and combinations of the above. Some of these indices are considered to be inadequate, inappropriate or impractical for some coal seam conditions, such as those with soft and friable coal. The Huainan Mining Group (Huainan) in China and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia have been jointly developing gas content based technologies to predict the risk of the outbursts. One of the major progressive achievements is a new method for determination of outburst gas content threshold values. The method utilizes empirical analyses, numerical modeling, and seam-specific knowledge . This paper describes the method and its application for the #11 Seam at Guqiao mine, Huainan.

Aug 1, 2013

By S. I. Saif

The Key Anacon deposit lies about 6 miles northeast of the Brunswick NO.6 mine of Brunswick Mining and Smelting Corporation. Geological mapping, especially in the well-exposed Nepisiguit River section, geophysical data, and information from extensive underground and some surface drilling show that the rocks at Key Anacon are similar in many aspects of stratigraphy and structure to those of the Brunswick Mine area. They include narrow beds of fine acid volcanic material interpreted to be metatuff and volcanogenic metasediments. The massive sulphide ore body at Key Anacon lies immediately above these acidic rocks, in association with other chloritic, sideritic or magnetic iron-rich metasediments. The iron formation, which is similar to that associated with other orebodies in the district, is overlain by massive andesitic material. Four phases of structural deformation have been recognized in the Key Anacon area; they are similar in intensity and style to those of the Brunswick No. 6 mine area. The orebody lies in a zone of complex isoclinal folding along the flank of a major F2 fold (Key Anacon Syncline) and in general appears to be stratiform. The ore occurs in probable F2 parasitic folds, and this suggests a complicated structural geometry superimposed on the original beds. The general similarity of the mineralization at Key Anacon, together with its occurrence with other iron-rich metasediments between a footwall of acid volcanic material and overlying andesitic rocks, is suggestive of stratigraphic time-equivalence with the Brunswick zone . If so, the metavolcanics at Key Anacon might have been derived either from a center within the main volcanic pile to the west or from a smaller local center active at the same time. Alternatively, the Key Anacon ore could have been formed during a much older volcanic cycle. The solution to this aspect of the problem is the subject of a continuing study.

Jan 1, 1978

By John Porritt, Alain Dorval

"TioMin Resources Inc. is evaluating the feasibility of exploiting the heavy mineral sands deposit at Natashquan on the north shore of the Gulf of St-Lawrence, Quebec. TioMin holds the exploration rights to 180 square kilometres, on which 1.6 billion tonnes of sands grading approximately 6% heavy minerals were outlined. The heavy minerals of value include magnetite, ilmenite/hematite, garnet, and zircon. An important part of this evaluation is the development and testing of a mineral separation flowsheet. Under a comprehensive mandate from TioMin, the Centre de recherches minerales (CRM) provided technical assistance to build and operate an on site primary concentrator pilot plant. This plant produced a 93 tonne concentrate, providing over 60 % heavy minerals. This concentrate was shipped to the CRM pilot plant in Quebec City. It was used for further flowsheet testing and for preparation of products and concentrates of heavy minerals with regard to marketing possibilities. This paper presents the flowsheet developed to produce these concentrates.IntroductionIn late 1992, an 11 tonne bulk sample of sand was collected from within the mineralized zone of the Natashquan deposit. This sample was processed over conventional spirals and wet tables at the pilot plant facilities of the Centre de recherches minerales (CRM) in Quebec City. A primary concentrate was produced, from which several 20 kg samples were forwarded to five research laboratories in North America and in Australia. Their tasks were to determine the mineralogical composition of this concentrate and the potential for recovery of marketable minerals from the heavy mineral sands. Satisfactory results obtained from this approach encouraged TioMin to proceed with a more detailed pilot plant program."

Jan 1, 1995

By I. A. Menshikh, S. A. Kotov, N. L. Shinkarkin

All the cycle for conversion of natural and reprocessed uranium of ROSATOM’s “TVEL” Fuel Company is concentrated at the Siberian Chemical Plant. Conversion capacities are located on two sites, i.e. the Radiochemical Plant, which refines feedstock, and the Conversion Plant, which produces uranium oxides and uranium hexafluoride. Liquid radioactive waste arising in the process, after pretreatment, is transferred to a dedicated national operator for underground disposal. Environmental strategies pursued by the Fuel Company involve the introduction of process solutions intended to eliminate liquid radioactive waste and convert it into a solid phase. In the 5–7 years coming, work will be performed to refurbish and upgrade conversion facilities of the Siberian Chemical Plant that will principally change its radioactive waste management scheme. This paper describes the current waste management scheme and sets out planned schemes for management of natural and reprocessed uranium waste, which will be implemented in the refurbishment of conversion facilities of the Siberian Chemical Plant. The new technologies for the management of liquid radioactive waste from uranium conversion described in the present paper have an undeniable advantage over the current technology mainly due to significantly less environmental harm.

Jan 1, 2020

By W. G. Schultz

"Sylvite's potash mine, which produces 8,000 tons of ore per day, probably ranks as one of the most highly mechanized and automated mining operations in the world. Employing, on a normal 10-hour production shift, one supervisor and a crew of seven operators, Sylvite is able to mine at an average rate in excess of 600 tons per hour. The ore is produced by two Marietta miners weighing 258 tons, the largest and heaviest pieces of equipment ever taken underground. The ore produced by these two Marietta miners is conveyed to the shaft area, cycled through a 15,000-ton storage system and hoisted to surface completely automatically. The operation of all equipment in the mine can be monitored and controlled from a central control panel located underground. Because Sylvite's mine is a new operation with equipment of a new design, the full potential of the operation has not yet been realized. The ultimate capability is clearly evident from the success Sylvite has had over the past year as the average mining capability has risen from 100 tons per hour to 600 tons per hour."

Jan 1, 1973

By G. Issid, J. McGinty, C. Lee, Y. Pepin

For more than a decade, Hatch has used process and logistics models to assist Rio Tinto Fer et Titane (RTFT) with capacity planning, debottlenecking, and optimization to help ensure design capability, capital effectiveness, and operational efficiency of the integrated production chain. Process models are used to optimize the physics-based aspects of the system, such as mass and energy balances, flow rates, yields, and equipment specifications. Dynamic logistics models are used to optimize how the various plant areas work together to achieve the desired ends and deal with such things as plant scheduling and synchronization strategies, sizing of buffers between processes, defining the required number of process and material handling units, and designing a plant layout that minimizes plant interferences and inefficiencies. The combined use of process models and logistics models enables the overall plant to be optimized from both a productivity and quality point of view, with each plant area working in harmony with one another to achieve targeted capacities and efficiencies. This paper describes the many benefits derived from such modeling efforts over the past 15 years for each of the major plant areas at RTFT: Beneficiation Plant, Smelter Plant, Steel Plant, UGS Plant, and Powder Plant (RTMP).

Jan 1, 2011

"This contribution is concerned with adaptive processing decisions, where the process parameters are optimally adapted to the varying properties of the material input stream. Our starting point is the geometallurgical paradigm that the varying properties of the input stream are considered known e.g. from a geometallurgical model of the mined ore body, and optimal processing parameters are computed from them, by finding the parameter seaming optimal in a computer simulation.This approach however has to work with a lot of uncertainties: The prediction of the geometallurgical ore parameters can only be done with some geostatistical uncertainty. The parameters themselves are only proxies for true ore properties. Model prediction can differ relevantly from actual process results, due to model simplifications. Due to these uncertainties the computed processing choices can turn out to be inferior to simple non-adaptive processing. In this contribution we focus on the uncertainty of the ore properties and analyse this effect systematically, by modelling this uncertainty effect mathematically and in computer simulations. The most important findings are:(a) Processing choices not taking into account the uncertainty sometimes even perform worse than simple non-adaptive processing, for the sole reason of ignoring the uncertainty effect.(b) Ore properties, not adequately reflected in the ore description, might require different approaches, in which the observed processing behaviour feeds back into process control.(c) Bayesian decision theory allows computing optimal processing choices combining the information from the mine (geostatistical predictions) and from the process feedback. These choices give much more robust choices and do not suffer from the drawbacks described for the simple approach we started from.These new approaches can substantially improve the performance of adaptive processing in existing plants."

Jan 1, 2016

By Renato Macciotta

The argillaceous formation known as the Opalinus Clay is host to the Mont Terri Underground Research Laboratory. The URL was developed to investigate the hydrogeological, geochemical and geotechnical properties of the formation. Underground excavations at the site are characterized by non-elastic and time-dependent deformations. Excavations trending perpendicular to the strike of the bedding presented relatively minor deformations, however, tunnels parallel to the strike of the bedding showed much larger non-elastic deformations. This paper presents an analysis of the measured response of a tunnel trending parallel to the strike of the bedding in Opalinus Clay. The measured convergence is compared to tunnel experience in weak rocks to assess the tunnel stability.

Jun 1, 2012

By F. Charette

The paper reviews the requirements of the instrumentation required to monitor mining excavations in a high stress environment, and the development plan to instrument the D-Bolt in such a fashion as to be able to follow the behaviour of the bolts in relationship to the ground movements and support performance. Recent field observations of D-Bolts under static and dynamic conditions are also presented. Also discussed is the assumed mechanical behaviour of the D-Bolt. D-Bolts are used in two (2) Canadian underground mines operating in high stress environments and tested in three (3) other operations.

Jun 1, 2012

By K. Chomyn, R. Veenstra, P. Zangeneh, Hatch Ltd., C. Van der Woude, H. Ghorbani

"The furnace is the heart of smelting operations, and therefore the performance, reliability, and campaign life of the furnace are critical considerations. Furnace refractory is exposed to high temperatures and other harsh operating conditions causing brick erosion, crushing, and cracking, typically limiting the furnace campaign life and requiring costly furnace shut-downs for refractory re-lining. Despite extensive study, the in-service thermal / mechanical stresses in these complex refractory systems are not generally well understood. Hatch has developed a thermal-mechanical finite element analysis (FEA) based furnace refractory modeling approach that allows for the quantification of refractory movements, load distribution, and thermal / mechanical stresses.Due to the complexity of the refractory system, a range of models are used to identify and assess damage mechanisms and design improvements, including: 2D models, to capture expansion and movement of individual bricks, changes to load paths, and thermal stresses; and 3D models, to include the effect of differential expansion between bricks in each course, and assess overall load distributions. The 2D and 3D analyses include the effect of nonlinear temperature-dependent properties, thermal expansion, movement of individual bricks with frictional contacts (i.e., gaps can open, bricks can slide), and brick tensile or compressive failure. Both as-built and damaged conditions can be investigated (e.g., after bath zone brick erosion), for circular and rectangular furnaces. 3D models also include papering and brick joint & interface action.Analyses using these models have shown the importance of thermal stresses, papering, and geometry / arrangement of individual bricks. Results have been used to identify and assess damage mechanisms, showing good alignment with furnace autopsy observations. By using this FEA-based approach to quantify the refractory design, the risk of damage can be significantly reduced, low-cost design changes can be identified, and the furnace campaign life can be extended.INTRODUCTIONThe furnace is the heart of smelting operations and therefore the performance, reliability, and campaign life of the furnace are critical to the success of the smelting operation. Furnaces are inherently exposed to high temperatures, often in excess of 1600°C (Holappa, 2004), and furnace operating power has progressively increased over time (Voermann, Gerritsen, Candy, Stober, & Matyas, 2004). The refractory system must withstand high temperature, high heat flux, and other harsh operating conditions. These conditions are particularly significant for the furnace hearth, and can lead to damage including brick erosion due to molten material flows, crushing due to thermal expansion loads, and cracking due to severe thermal gradients within the bricks. Refractory damage typically limits the furnace campaign life, requiring costly furnace shut-downs for refractory re-lining (repair or replacement). In some cases the refractory may lose integrity causing damage to nearby equipment and harm to personnel."

Jan 1, 2016

By M. R. MacIver, M. P. Pawlik

"An image analysis method based on chord length distributions is applied to the batch settling of polyacrylamide flocculated kaolin suspensions. Two features of the interaggregate void space, the void chord length distribution mean and the white-to-black distribution ratio are extracted from an image series obtained over the two hour settling experiments. This approach produces three signal values, from two different probability distributions that can be measured as an indication of underlying sediment bed density and aggregation state. Further work is required on the physical interpretation of the signal, the image acquisition conditions, and the parameter selection methods. It is suggested that this chord length based feature extraction technique may be a useful signal to monitor during batch settling or thickening.INTRODUCTIONFew in situ techniques are available that can be used to directly measure aggregate properties within sediment beds in thickeners or secondary settlers. Typical process variables monitored include rake torque and height, bed level and pressure, feed rate and density, underflow rate and density, settling rate, and overflow turbidity; yet these process variables are only weakly related to process dynamics (Concha et al. 2014). Additional process monitoring signals, based on the direct measurement of aggregate properties could improve solid-liquid separation control and allow the extraction of more detailed information from batch settling experiments.Several optical methods exist for measurement of moving suspensions of aggregated solids in the dilute concentration regime, such as focused beam reflectance measurement (Peng and Williams 1994), and the turbidity fluctuation method (Gregory 1985). In the more concentrated region of a thickener, acoustic backscatter penetration and attenuation measured with an acoustic probe and changes in the underlying solid concentration in the highly concentrated, near-bed region of a thickener as a function of height and time (Hunter et al. 2012). While machine vision for froth monitoring has been thoroughly studied with at least five commercialized technologies (Aldrich et al. 2010), its’ application to the study of thickening has been limited."

Jan 1, 2016

By M. Mirnezami, J. A. Finch, M. S. Hashemi A.

The surface of -30µm silica suspension (2% v/v) treated with 100 ppm Mg2+ at pH 11 was fully coated with Mg(OH)2. Under this condition, the silica is strongly positively charged (+30 mV) and the suspension is dispersed. Subsequent addition of Ca2+ promoted aggregation and reduced the surface charge. At this pH calcium is present as Ca2+ and CaOH+, i.e., positively charged ions interacted with the positive surface. Aggregation by a chemical bridging mechanism is proposed. The observation may be relevant to the widespread practice in mineral processing of adding lime to promote aggregation and settling in concentrate thickeners.

Jan 1, 2004