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By M. A. Belokrys, F. O. Milovich, D. D. Aksenova, V. A. Ignatkina, V. A. Bocharov, A. A. Kayumov

Copper remains one of the most sought-after metals in the industry. Tennantite (Cu12As4S13) and tetrahedrite (Cu12Sb4S13) that occur in pyrite copper, copper-zinc and polymetallic ores are an additional reserve for increasing technological parameters of flotation. Pyrite mass (85% and more) has similar flotation properties to other sulfide minerals, and imperfection of reagent regime is a common problem that occurs during quality copper concentrate processing. Due to tennantite's and chalcopyrite's differences in flotation properties with butyl xanthate at pH > 10, tennantite often reports to the flotation tails. Hight alkalinity of the medium increases the oxidation level of sulfide minerals, thus increasing the concentration of S2O3 2-, SO3 2- SO4 2-. At processing facilities in the Russian Federation, the concentration of thiosulfate ions in pulp is in the range of 0.5 to 1.5 g/l and higher, which leads to a decrease in flotation activity of the tennantite. The effect of butyl xanthate (as standard), thionocarbamate, dithiophosphate and M-TF (a mixture of dithiophosphate and thionocarbamate) on monomineral (tennantite and pyrite) flotation in the presence of sodium thiosulfate was studied. The variable parameters of the "thiosulfate-collector" flotation complex were thiosulfate concentration (100-900); pH (8-12,5). The scientific methods included contact angle for hydration assessment; TEM for surface studies; UV spectroscopy and iodometric titration for solubility control. Comprehensive studies have established a connection between the concentration of thiosulfate ions and tennantite flotation selectivity. Flotation activity of tennantite is higher at pH 8 with a thiosulfate concentration under 300 mg/l. Pyrite remains active with butyl xanthate under the same conditions. TEM images of the surface films of the collectors on pyrite were acquired at pH 8. The MTF provides the biggest difference in adsorption, wettability and flotation activity between tennantite and pyrite at pH 8 and thiosulfate concentration under 300 mg/l, in comparison with butyl xanthate. The results of the research will be applied to improve selective reagent regimes of tennantite minerals flotation. Keywords: Tennantite, pyrite, chalcopyrite, sphalerite, flotation, sulfhydryl collectors, thiosulfate, adsorption, mechanism, reagent regime

Jan 1, 2020

SACPE has asked the Journal to bring the following points to the notice of members who are about register with SACPE. When to Apply There is no set time to apply for registration. Engineers should apply when they believe that their training has met all the requirements of Policy Statement No. 1/3. Pitfalls Remember that it is the applicants' training that must be evaluated, and this requires the avoidance in the application of vague generalities such as 'My duties were design plant including its economic evaluation' or 'I was engaged in . . Requirements An example of what is required can perhaps best illustrate the point.

Jan 1, 1982

By F. Riedel

In May 2009 a test work programme was carried out at the sorting laboratory of CommodasUltrasort in Germany which was aimed at establishing the efficiency of X- ray transmission sorting for the recovery of unliberated diamonds in a size range of +8mm. A PRO Tertiary XRT belt sorter with a working width of 600mm and a belt speed of -3mJs was used for the test work. Dual energy X-ray transmission sorting is a type of sensor-based sorting which uses an X-ray scanning system, The attenuation of the transmitting X-rays is measured at two different energy levels, Thereby it is possible to eliminate the effect of the particle thickness on the measurement result. The effective measurement results in a classification by elemental order based on the periodic table.

Jan 1, 2010

By J. Petersen, H. Naderi, H. Zare, M. H. Nikzad, M. Karimi

In the copper electrorefining process, the dissolution of anodes is significantly reduced or even stopped when the passivation phenomenon occurs. The results of this phenomenon are increasing energy consumption, residual formatting, and voltage levels in the cell. In this study, the electrochemical behaviour of blister copper in the presence of sodium persulfate (PDS) was studied. The electrochemical methods of LPR, Tafel, and Electrochemical Impedance Spectroscopy (EIS) were used. The results showed that the addition of sodium persulfate activates the electrode surface and increases the open circuit potential. In the presence of PDS, the polarisation resistance of the electrode shows an increasing or decreasing tendency, based on the PDS concentration. This tendency is probably due to the formation of surface layers (such as slime layer or copper sulfate) and dissolution of this layer at various concentrations of PDS. The lowest polarisation resistance of 1.8 ohms and the highest corrosion current of 60.6×10-3 and 36.6×10-3 A/cm2 from LPR and Tafel techniques respectively were obtained at the concentration of 40 g/l PDS. Based on the results of potentiodynamic and electrochemical impedance spectroscopy tests, the addition of sodium persulfate to the solution reduces the corrosion resistance, therefore the passivation time of the blister copper anode increases. Keywords: Blister copper, electrorefining, sodium persulfate, anodic passivation

Jan 1, 2020

Caving is the lowest cost underground mining method provided that the draw point spacing, draw point size, and ore-handling facilities are designed to suit the caved material, and that the draw point horizon can be maintained for the life of the draw. In the near future, several open-pit mines that produce more than 50 kt per day will have to examine the feasibility of converting to low-cost, large-scale underground operations. Several other large scale, low-grade underground operations will experience major changes in their mining environments as large dropdowns are implemented These changes demand a more realistic approach to mine planning than in the past, where existing operations have been projected to increased depths with little consideration of the change in mining environment that will occur. As economics force the consideration of underground mining of large, competent ore bodies by low-cost methods, the role of cave mining will have to be defined In the past, caving was generally considered for rockmasses that cave and fragment readily. The ability to define cavability and fragmentation, the availability of large, robust load-haul-dump units, a better understanding of draw-control requirements, improved drilling equipment for secondary blasting, and reliable cost data have shown that competent orebodies with coarse fragmentation can be exploited by cave mining at a much lower cost than by drill-and blast methods.

Jan 1, 1994

"Chairman: Dr N. G. W. Cook Rapporteur: Mr M. P. RobertsPapers:Planning open pit mining operations using simulation by A. Bauer and P. N. Calder Simulation for control of underground liquid flow by G. N. Pitts and P. B. CrawfordEvaluation of production strategies in a group of copper mines by linear programming by P. H. Williams, J. N. Brooke and D. M. PoulterAn equipment maintenance system by D. W. Dean and J. A. RyderTaken as a whole, the difference between the four papers in this session were perhaps more illuminating than their similarities. The titles of the first and second papers contained the word 'simulation', and in both papers random number generation was relied upon in the selection of inputs from empirical distributions, but the nature of the models to which these values were inputs were quite different. The third paper displayed another method of uniting the empirical and the theoretical in a linear programming formulation whose matrix coefficients were measured empirically, and here some apt remarks on computer implementation were included. This paved the way for the last paper which abandoned all theoretical pretensions in favour of a detailed description of computer implementation and perhaps as a result gave rise to the most feeling audience participation.The systems mentioned were developed for the iron, petrol, copper and gold producing industries in the US, Canada, Zambia and South Africa..As with all the parallel sessions, contributions from the floor may have been limited by the shorter time available to delegates to acquaint themselves with the papers before the session. In spite of this, and due largely to the active chairman¬ship of Dr Cook, the discussion during the session which is summarized here contributed much to the information contained in the papers themselves.In his presentation, Dr Calder summarized his paper. He expected that simulation would be used in future on an almost universal basis in open pit mining. It could contribute new knowledge more cheaply than experimentation in the flea For example, this study had shown what was previously thought to be a matter of more shovels and trucks was really a blasting problem, and improving blasting had increased production to the desired level. The simulation had shown that uniformity of truck performance was a desirable factor. It had also been used to study the advisability of a dispatching system.Dr Ramani contended that where equipment characteristics were available, deterministic standard simulation could adequately simulate systems in which interference occurred. Operator performance could be measured against perfor¬mance curves predicted by standard simulation and poor operators spotted and retrained. The present system did not take into account variability in truck loading, for instance. Dr Calder replied that if the number of variables was large, the standard approach became too complicated for operating personnel to follow. He admitted he had not tried it. The variability of truck loading could be coped with easily using the Monte Carlo approach. Operator variability was already incorporated because the time studies are actual."

Jan 1, 2014

By L. Thomas, D. Muteba, L. I. Nsenga, B. Mbao, G. Longo Banza

Owing to the high ore grades in the African Copperbelt and variable acid consumption, agitated leaching is common practice and is used more widely in Africa than in other regions. Two common challenges for agitated leach–solvent extraction circuits are higher presence of colloidal silica in the pregnant leach solution and elevated levels of total suspended solids. Both can negatively affect the physical and metallurgical performance of the solvent-extraction circuit, and lead to higher processing costs or reduced copper production. Operating in organic continuity is preferred to address such challenges, but is not always possible: additional treatment options may be advantageous. For this reason, Solvay recently introduced ACORGA® CR60LT, a new chemical additive to address these concerns. Continuous addition to the pregnant leach solution improves physical performance without negatively affecting Cu transfer or cathode quality. Results and benefits from commercial utilization of ACORGA® CR60LT at different operations in the Copperbelt are reviewed

Jan 1, 2023

By C. A. Green, M. A. T. Cocquerel, R. T. Gates

"Engineering studies by Selection Trust, Limited, initially in connection with the development of a copper and nickel deposit for Bamangwato Concessions, Limited, and subsequently for several other clients, have required a large number of metallurgical design calculations. The flash smelting process, developed by Outokumpu Oy in Finland, has been selected as the most suitable method for these projects and the computer programs described in this paper have been developed to facilitate the computation.The data required by the programs arc the chemical and mineralogical analyses of the concentrate, gangue and flux materials and the specification of possible fuels. The required grade of furnace matte is set as the main design parameter and the programs calculate detailed heat and material balances for the smelting process."

Jan 1, 2014

One of the key issues facing gold producers is the management of cyanide and the implementation of the International Cyanide Management Code. Many operations now use cyanide destruction processes to ensure that the material being discharged to the tailings dam is compliant with regulatory requirements and the International Cyanide Management Code. One of the problems for operations is the quantification of both cyanide species and their reaction products throughout the leach and destruction circuits. Therefore methods have been developed utilizing high performance liquid chromatography (HPLC) to measure free cyanide, cyanide complexes of metals such as copper and iron, and other species formed from reactions in leaching and cyanide destruction, including cyanate, thiocyanate, and sulphur species (eg. sulphite, thiosulphate and sulphate). This enables a complete mass balance for cyanide and sulphur in both leaching and cyanide destruction. This paper outlines the methodology which has been developed and discusses the application of these methods in the fundamental research currently being conducted on the impact of sulphide minerals in cyanidation and cyanide destruction chemistry.

Jan 1, 2009

By J. D. Swanepoel, S. Horn, C. J. Badenhorst

Diesel particulate matter (DPM) is the particulate component of diesel exhaust, which includes diesel soot and aerosols. When released into the atmosphere, DPM can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometer range of 100 nanometres. The main particulate fraction of diesel exhaust consists of fine particles and because of their small size, inhaled particles may easily penetrate deep into the lungs. The rough surfaces of these particles make it easy for them to bind with other toxins in the environment, thus increasing the hazards of particle inhalation. DPM is a significant health hazard in underground mining operations, where the use of dieselpowered equipment in confined spaces can lead to high levels of exposure among people working in these environments. Classified as a carcinogen by the International Agency for Research on Cancer (IARC), DPM has been linked to severe health effects, including respiratory and cardiovascular diseases, as well as an increased risk of lung cancer. Effective management of DPM is essential not only for protecting people’s health but also for ensuring regulatory compliance, maintaining operational efficiency, and safeguarding the long-term viability of mining companies.

Mar 5, 2025

By Z. Nzimande

The Constitution of the Republic of South Africa advocates the importance of sustainable economic development and justifiable environmental consciousness by business. The government needs to ensure that every citizen of the Republic has access to an environment that is protected, pollution free, and sustainable by enacting certain regulations. However, there are more than 5 700 derelict and unrehabilitated mines of all types in South Africa. Former asbestos operations were among the first to be targeted for clean-up under the programme instituted by the Department of Mineral Resources (DMR), owing to the proven direct impact of asbestos pollution on health. This paper seeks to investigate the challenges faced by the coal sector as far as mine rehabilitation and closure is concerned. For the purpose of this paper rehabilitation is defined as per the Chamber of Mines Rehabilitation Guidelines publication, which defines rehabilitation as putting the land impacted by mining activities back to a sustainable and usable condition. Some of the current rehabilitation challenges are technical skills (know-how), leadership focus, poor planning, cost saving initiatives, and the government's lack of capacity to enforcement rehabilitation requirements. It is imperative that mining companies identify rehabilitation as a critical strategic pillar that directly influences license to operate. The case study evidence indicates that relevant policies, appointment of accountable people, sufficient leadership support, and the correct choice of rehabilitation equipment can assist to improve the rehabilitation and land management challenge.

Jan 1, 2012

By G-L. Wu, X-B. Liu, C-Y. Zhou

"The static recrystallization behaviour of Ti-Nb microalloyed high-strength steel during hot deformation was studied by conducting double-hit hot compression experiments using a Gleeble-3500 thermomechanical simulator. The effects of deformation temperature, strain rate, strain, and initial austenite grain size on the static recrystallization fraction are discussed. The static recrystallization kinetics were modelled, and the results show that the static recrystallization fraction increased with deformation temperature, strain rate, and strain and interpass time. The static recrystallization activation energy Qs was 326.05 kJ mol-1. Comparison of the experimental results and predicted results indicates that the effects of deformation parameters on the static recrystallization in multistage hot deformation are significant. The predicted results are in good agreement with the experimental results. IntroductionIn hot-forming processes, complex microstructures are often induced by multiple hot deformation mechanisms (Zhang et al., 2014; Liang et al., 2015). The softening behaviour during hot processing has generated considerable interest because component properties are influenced significantly by the corresponding microstructural evolution (Wu et al., 2010). It is well known that dynamic recrystallization (DRX); metadynamic recrystallization (MDRX), which occurs by the growth of DRX nuclei during intervals of deformation; and static recrystallization (SRX), which occurs by nucleation and growth during the intervals of deformation, can significantly alter the austenite grain size (Chen et al., 2015. Chen, Sui, and Cui, 2014; Mao et al., 2014). The long interpass times allow complete SRX to take place if the steel is being rolled above the interpass recrystallization stop temperature (Tnr), i.e. in the absence of carbonitride precipitation (Siciliano, 2000). In recent research, microalloying technology coupled with new-generation thermomechanical control processing (NG-TMCP) has proved efficient in achieving the proper balance between strength, toughness, ductility, and formability by means of a suitable combination of chemical composition and thermomechanical treatment parameters (Shukla et al., 2012; Bandyopadhyay et al., 2011). The alloying elements Nb, V, Ti are widely used in high-strength low-alloy (HSLA) steel to achieve the desired strength and toughness properties with solid-solution strengthening, precipitation hardening, grain refinement, and dislocation strengthening (Opiela, 2014; Chen and Yu, 2012). The wide applicability of alloying elements in HSLA steel is due to the fact that heat treatments are not required after forming of the parts, which results in time and cost savings."

Jan 1, 2017

By H. W. J. P. Neomagus, J. R. Bunt, T. S. Mthombo, C. A. Strydom

"Low-cost calcium lignosulphonate (CL), which is a byproduct of the wood pulping industry, was investigated as a potential binder during laboratoryscale pelletization of inertinite-rich high-ash coal fines from the Highveld Coalfield of South Africa. Coal-binder mixtures containing between 1 and 15% calcium lignosulphonate were prepared, pressed, and ultimate, proximate, porosity, XRD, and XRF analyses obtained. It was found that increased pressure during pelletization results in increased attractive forces, due to increased interparticle contact areas. FTIR analysis showed that chemical interactions occur between coal fines and the binder, as evidenced by the formation of new C-O ether-type bonds. The presence of moisture during pelletization enhanced surfactant activity of the binder. Chemical interactions between the coal and the binder seem to be mainly electrostatic, driven by Ca2+ from the calcium lignosulphonate, which may act as a bridge between the anionic parts of the binder and the surface of the coal. IntroductionCoal has over the years remained South Africa’s major energy source, with over 90% of the country’s electricity being produced via coal-fired processes (Arndt et al., 2016). Sasol’s coal conversion technology alone provides more than 40% of South Africa’s liquid fuel requirements (van Dyk, Keyser, and Coertzen, 2006). The production of high-grade coal requires the processing of run-of-mine (ROM) resources by a combination of processes which include crushing, screening, and washing (Radloff, Kirsten, and Anderson, 2003). These processes result in the generation of coal fines (< 0.5 mm) which, until recently, have been discarded into slimes dams (le Roux, Campbell, and Smit, 2012). Several issues are associated with slimes dams, among which are the costs of transportation of these fines from the place of origin to the discard point (often a considerable distance), and the potential environmental effects due to seepage of toxic materials into surrounding ecosystems (Clausen, 1973).Consequently, utilization of these coal fines is an area of great interest. Mechanical densification of fine coal by means of pelletization and/or briquetting to larger sizes for use in technologies that require lump coal, such as chain-grate stokers and fixed-bed gasifiers, has been shown not only to reduce environmental risks (Mangena et al., 2004), but also to significantly reduce storage and transportation costs (Mani et al., 2001). Pelletization is the process by which solid particles are consolidated into uniform, usually hard, impact-resistant agglomerates, rendering them useful as a fuel with sufficient calorific value for domestic and industrial utilization (Finney, Sharifi, and Swithenbank, 2009)."

Dec 1, 2018

By T. Moyo

"The oxidative leaching of chalcopyrite in ammoniacal solutions has been evaluated using electro-analytical techniques and controlled bulk leaching studies. The anodic dissolution process has been established to be a sevenelectron transfer process under nitrogen in ammonia–ammonium sulphate solutions and ammonia–ammonium carbonate solutions, which suggests that the sulphur is oxidized to thiosulphate and the copper and iron released as Cu+ and Fe2+ in these systems. The deportment of Fe2+ and S2O3 2- is affected by choice of the ammonium salt used in the leaching process. In the perchlorate salt, only five electrons are transferred, supporting formation of different sulphur species as proposed for the sulphate and carbonate salts. Scanning electron microscopy and energydispersive spectroscopic analysis of the mineral surface after leaching indicate presence of an iron–sulphur surface layer completely free of copper in the sulphate system, an iron-rich surface layer in the perchlorate solutions, and absence of surface layer build-up in carbonate solutions. XRD analysis of a bulk leach residue from leaching in ammoniaammonium sulphate solutions showed the surface layer to be mostly amorphous (90%). The crystalline content (10%) is composed of 95% polymorphs of anhydrous iron oxide hydroxide FeO(OH). Choice of ammonium salt and the hydrodynamic environment of leaching have been shown to influence the presence or absence of the surface product, as well as its nature. IntroductionHydrometallurgical processes for copper extraction provide a viable route to recover the metal from mixed and low-grade ores, as well as overcome the environmental challenges faced by the traditional pyrometallurgical processes. Chalcopyrite is not only the most abundant of the copper sulphides, but also the most stable, making it recalcitrant to hydrometallurgical processes. Hence, hydrometallurgical processing of chalcopyrite continues to be an attractive area of research due to the vaguely understood surface chemistry of the mineral in different aqueous media. Different routes for hydrometallurgical treatment of chalcopyrite can be followed. These include thermal treatment prior to leaching, direct leaching and direct electrochemical leaching (Venkatachalam, 1991). Direct leaching of chalcopyrite can be carried out in various solution systems, as reviewed by Roman and Benner (1973) and Venkatachalam (1991). Ammoniacal solutions are attractive and effective lixiviants that form stable amine complexes with some base metal cations while rejecting iron. Leaching of chalcopyrite in ammoniacal solutions in the presence of an oxidant is possible due to the stabilization of copper (I) and copper(II) by ammonia at elevated pH levels. In oxygenated ammonia solutions, it has been suggested that chalcopyrite dissolves according to Equation [1] (Beckstead and Miller., 1977a):"

Jan 1, 2016

By J. Jacobs

The three-product cyclone was originally developed in Russia and is now extensively used in China. The cyclone has recently entered the South African coal industry, and with the obvious advantages that this item of process equipment offers our ever-evolving industry it is safe to assume that it will add value to dense medium circuits in South Africa. Some of the possible applications include: ? Producing multiple products using a single dense medium circuit. These can typically be a primary product with calorific value of 27.50 MJ/kg and a secondary (middling) product with a calorific value of 22 MJ/kg ? High-density separation with a low circulating medium density. Anglo Thermal Coal and Exxaro have pioneered the use of these units at Umlalazi and New Clydesdale respectively. Extensive test work has been performed at Umlalazi to determine the efficiency of the unit and to determine how it compares with the conventional DSM (Dutch School of Mines) cyclone. Some people in the coal industry were initially sceptical and expected the performance of the three-product cyclone to be inferior to that of the conventional dense medium cyclone. The results of the test work have, however, shown that the efficiency of the unit is comparable to that of the cyclones currently employed. A valid concern expressed is the control over the cut-point density of the second stage separation, and work is on-going to find the optimal way to control the secondary separation density. Theoretically, the secondary separation density can be manipulated by changing the orifices of the unit, especially the spigot of the secondary stage. This remains to be proven, and a series of tests is currently being planned. Whatever the result of these tests may be, the three-product cyclone definitely has a place in the South African coal processing industry as it offers a low OPEX and CAPEX solution for producing multiple products from a single circuit, as well as the ability to operate at very high separation densities, while making use of low-density circulating medium. Keywords dense medium separation, DSM, three-product cyclone, coal processing.

Nov 1, 2013

By S. T. L. Harrison, M. A. Fagan-Endres, M. D. Odidi

This paper investigated the ability of eight common hydrodynamic models – tanks in series (TIS); three compartmental model configurations (Comp-1, Comp-2 and Comp-3); advection dispersion (AD); piston exchange (PE); piston exchange-diffusion variant (PE-D) and piston dispersion exchange (PDE) – to simulate residence time distribution (RTD) data generated from tracer tests conducted on a packed bed composed of different size fractions of malachite ore. The chosen materials were packed into 0.1 m internal diameter columns to a depth of 0.155 m and drip irrigated at 5.11 L/ m2.h. The four size fractions tested were: 1 – 2 mm, 2 – 2.8 mm, 4.75 – 5.6 mm and 13.6 – 16 mm. Step-up tracer tests were conducted using potassium chloride. The results showed that an increase in the particle size of the malachite ore had little effect on overall bed porosity but resulted in significantly lower values of liquid holdup. Two of the monoporosity models tested, TIS and Comp-2, were the most affected by the changes in bed size fraction due to their inherent inability to cope with high degrees of non-ideal flow present in the larger particle systems. The dual porosity models performed relatively better with the dominant trend being a reduction in dynamic to total liquid holdup as particle size increased. Of all the models tested, the PDE and TIS models were the best and worst performers respectively, with R2 values averaging at 0.997 and 0.679 across all experiments respectively. Though the Comp-1, Comp-3 and PE-D models also performed well, the addition of the dispersion coefficient to take the axial spread of fluid molecules into account added a layer of complexity that allowed the PDE model to perform relatively better than the other dual porosity models. Keywords: Heap leaching, packing material, hydrodynamics, malachite, PSD, modelling

Jan 1, 2020

By J. le Grange, M. Tullmin, A. Strauss, F. P. A. Robinson, C. A. O. Henning

An experimental feritic stainless steel with a chromium content of 40 per cent was welded by laser and electron beam (EB) welding processes. These techniques were found to be particularly suited to the welding of this alloy in that the impact toughness of the weld metal and heat-affected zone (HAZ) of the laser welds compared favourably with those of the parent aloy. When the EB process was used, the impact toughness of the weld metal was over 180 J/cm2. Grain growth in the HAZ was minimal for welding with these two processes. Corosion tests, conducted in a solution consisting of 20 per cent sulphuric acid and 100 p.p.m. of potassium thiocyanate, and In a highly corrosive industrial solution, indicated that the laser and EB welds were free of sensitization effects, thus confirming the metalographic results.

Jan 1, 1989

By M. J. Santofimia

Multiphase microstructures in steel have been intensively studied in the past years, but combining non-equilibrium phases still offers a great potential for further development of these steel grades. Thus, improved combinations of mechanical properties can be obtained with microstructures formed by bainite or martensite, in combination with retained austenite. In particular, microstructures on the basis of carbon-depleted martensite and retained austenite can be produced by the very promising production process named quenching and partitioning (Q&P). Originally, the Q&P process aimed to avoid the formation of bainite during the heat treatment. However, the process does provide the possibility for (carbide-free) bainite formation during the partitioning step, i.e. in the presence of martensite. This article evaluates this approach, considering thatthe formation of bainite from austenite is strongly influenced by the preceding formation of martensite. Although the accelerating effect of the presence of martensite during bainite formation has been observed, it is not yet fully understood, and experimental and theoretical studies are being performed in order to come to a more effective exploitation of these processes for the formation of multiphase microstructures.

Jan 1, 2013

By Maggi Loubser

"In a technologically advanced era, where process control is accurately maintained within the smallest error margins, and accuracy and precision are continuously improved, sampling is still left to the lowest paid employee in the company without training him or her properly to understand the relevance and importance of the task. In this paper the objectives of sampling in a process control environment is discussed and an attempt is made to link it to the theory of sampling. Some of the practical problems associated with implementing theoretical sampling principles in an industrial environment will be elucidated and some examples given on how compromises are made. Different methods of sampling will be discussed with real life examples from different manufacturing industries."

Jan 1, 2014

By W. J. Vlasblom, A. M. Talmon, A. J. Nobel

In initial laboratory tests with a travelling submerged jet on artificially prepared clay it was found that the cavity depth is dependent on the stagnation pressure of the jet and the undrained shear strength of the clay. In addition, it has been observed that the increase in cavity depth with jet pressure is stronger at higher jet pressures. It is assumed that this can be explained by cavitation of the jet at higher jet pressures. At cavitation a cone of bubbles is formed around the jet, which reduces the exchange of momentum between the jet and the surrounding water. This results in a higher jet velocity and a higher stagnation pressure at a specified distance from the nozzle exit. In literature, no relation between the jet pressure of a free submerged cavitating jet and stagnation pressures was found. Additional tests were carried out to determine this relationship. Because practical dredging occurs at relatively large water depths, these tests were performed in a pressure vessel at different pressure levels. It is concluded that the efficiency of a jet (defined as the stagnation pressure at a certain distance divided by the jet pressure), for stand-off-distances smaller than 45 times the nozzle diameter, increases significantly by cavitation in comparison to the non-cavitating situation. However, the jet pressure required for a fully developed cavitation cone increases strongly with water depth. At dredging depths of 20 m and more, the necessary jet pressures are higher than normally applied in dredging practice. Thus in spite of the importance of cavitation in laboratory tests at atmospheric pressure, in normal dredging practice cavitation is of less importance.

Jan 1, 2007