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By David Hake, David Salisbury

The Drainage Services Department (DSD) of the Hong Kong SAR Government commissioned the design and construction of the West Kowloon Drainage Improvement, Stage 2, Phase 2, Kai Tak Transfer Scheme (KTTS) project in 2000 to relieve potential flooding in Mong Kok caused by the insufficient capacity of the existing storm water drainage system. The KTTS involves construction of a 1.5km,4.4m drainage tunnel and a 450m long box culvert, running from Waterloo Road near Hereford Road to the existing Kai Tak Nullah in San Po Kong. This paper describes the design and construction of; the bored tunnel through both hard rock and soft ground using a slurry Tunnel Boring Machine (TBM), six associated access shafts, a connection structure at Waterloo Road and the box culvert connecting the bored tunnel to the outfall at Kai Tak nullah. Details will be provided on the contractor’s alternative designs adopted during the contract including the use of fibre reinforced shotcrete as one-pass temporary and permanent support for three of the shafts and modifications to the Engineer’s design for the box culvert structure.

Jan 1, 2005

By S. V. Rungan

Since 1994, South Africa has been the subject of international attention, especially in regard to its transformation initiatives, which aim to redress the post-apartheid imbalances. Mining, as a major employer and one of the major industries in South Africa, has been the focus of the government?s Black Economic Empowerment initiative with the introduction of the Minerals and Petroleum Resources Development Act and the Broad?Based Socio?Economic Empowerment Charter for the South African Mining Industry. The historical background to South Africa?s transformation and the role of the mining industry are pivotal to an appreciation of certain aspects of the Minerals and Petroleum Resources Development Act and the Broad?Based Socio?Economic Empowerment Charter for the South African Mining Industry. The issues around Black Economic Empowerment and the enabling of a smooth transition to the South African mining industry of the future are explored in this paper.

Jan 1, 2005

By N. E. Yasitli

There is a considerable amount of lignite reserve in the form of thick seams in Turkey. It is rather complicated to predict the characteristics of strata response to mining operation in thick seams. However, a comprehensive evaluation of ground behaviour is a prerequisite for maintaining an efficient production, especially when top coal winning by means of caving behind the face is applied. A comprehensive modelling of deformations and induced stresses is vital for the selection of optimum production strategy. In this study, numerical modelling and analysis of a longwall panel at Omerler underground coalmine have been carried out by using the software called FLAC3D developed based on the finite difference technique. Firstly, a 3-D numerical model of the M3 panel has been prepared. Secondly, induced stresses formed around the longwall face have been determined as a function of face advance where the face was located at the bottom of thick coal-seam. Results obtained from modelling studies have revealed that the front abutment vertical stress was maximum at 7 metres in front of the face and magnitude of front abutment stress was found to increase up to a distance of 200 metres away from the face start line. As the face was further advanced after 200 m from the face start line, there was not any significant change in the characteristics of front abutment stresses. Results of numerical analysis of the panel were in good agreement with in situ observations.

Jan 1, 2005

By Baruch Grinbaum, Edwin Bwalya, Robert Minango, Deogratias Bukunkwe

Solvent extraction of Cu from acidic leach, using an oxime extractant, e.g. LIX 984 or Acorga is a well known and established process. As the process advances, Cu is extracted to the solvent and is replaced by H+ in the aqueous phase. At high acidity the distribution coefficient of Cu between the solvent and the aqueous phase decreases, and eventually relatively high concentration of Cu remains in the raffinate, regardless of the number of equilibrium stages. In many processes this phenomenon is immaterial, as the raffinate returns to the leaching and no copper is lost. But when the copper raffinate is used for processing of additional metals, minimal concentration of Cu in the raffinate is essential for an effective process. The recommended process includes three steps: 1. SX-1: Standard extraction of Cu with oxime. The resulting raffinate contains about 6-8 g/L Cu and 50 g/L H2SO4. 2. SX-N: Extraction of most of the acid into an amine-based solvent, and stripping it with a base, e.g. aqueous ammonia, caustic, Na2CO3 etc. The extraction removes no metals, but decreases the concentration of acid from 50 to 10 g/L. 3. SX-2: Extraction of the neutralized solution once more with oxime, to remove the residual copper. Such a process enables one to get down to 100-150 ppm Cu in the final raffinate. This process was developed and tested in the R&D facility in Chambishi Metals plc, by a joint team of Chambishi & Bateman, using Cognis LIX 984N and real solutions from the plant. In the laboratory scale, the equilibrium isotherms for SX-1, SX-2 and the neutralization were developed. Computer simulation of the results showed that the optimal configuration is two stages for both extraction and stripping for SX-1. For SX-2 2-3 stages of extraction and two stages of stripping are needed. The stripping stages may be common to both SX-1 and SX-2. The neutralization of SX1 raffinate was tested both by conventional precipitation with lime and by extraction with Alamine based solvent extraction and stripping with a solution of 10% NaOH. For the SX-N only one stage was needed for both the extraction and stripping. The bench scale pilot plant was run for both SX-1 & SX-2. The results were very similar to the simulated ones, and the configuration of 2E2S for SX-1 and 3E=2S for SX-2 delivered the required raffinate with less than 150 ppm Cu.

Jan 1, 2005

By N. Vayenas, G. Yuriy

"The combination of a predictive reliability assessment model and discrete-event simulation can be an effective methodology to study the impact of equipment failures on the capacity of production systems in mines. In our case, a predictive reliability assessment model using genetic algorithms is combined with a discrete-event simulation model to analyze mine equipment systems.Discrete-event simulation involves modelling of real-life systems based on variables and events that occur or change at distinct points in time. The Simul8 simulation software, by Visual Thinking, is used in this research. It is a two-dimensional (2D), discrete-event simulation/ animation software tool for creating realistic depictions of manufacturing and materials handling systems.The simulation model developed for the purpose of this research represents a typical two-level, sub-level stoping section of an underground mine in the Sudbury region in Ontario, Canada. This 2D model was created to assess the impact of equipment failures to a mine’s production throughput. In more detail, using mean time between failures (MTBF) data of scooptrams derived from a reliability assessment model based on genetic algorithms, LHD failures are incorporated into the simulation model. These failures cause production interruptions to the development cycle and consequently loss of hauling capacity.Another purpose of this research work is to demonstrate how low-cost simulation tools such as Simul8 can be successfully applied to model underground hard rock mining operations. The research discussed in this paper is carried out by the Laurentian University Mining Automation Laboratory (LUMAL)."

Jan 1, 2005

By J Rubio

This work presents design features of an innovative in-line mixing helical (coiled) reactor for flocculation and flotation as a solid-liquid separation process for suspended particles (including liquid droplets). The device has been named flocs generator reactor (FGR), a compact system whereby the flocculation of particles is assisted by the kinetic energy transfer from the hydraulic flow through the reactor and/or by the injection of microbubbles (30 - 70 ¦m). The flow mixing presented a plug flow regime with a low dispersion degree, promoting the required hydrodynamic conditions to disperse the polymer flocculant (cationic polyacrylamide) and to generate æstrongÆ flocs of Fe(OH)3 or clays (as colloidal model systems) with aggregation using an anionic polymer, Al2(SO4)3 and poly aluminium chloride (PAC), and oil emulsions destabilisation with a high molecular weight cationic polymer. The solid-liquid separation of the flocs was then achieved either by settling or by flotation with microbubbles. This paper discusses advances in this new in-line flocculation-rapid flotation device to remove æaerated aggregatesÆ, aggregates with entrained and entrapped bubbles. Studies were carried out with different models of FGRs (varying the length:volume ratio) and process efficiency (mainly kinetics) evaluated as a function of polymer concentration and some operating parameters, namely, feed flow-rate, air:solids ratio and residence time. Results showed that the aerated flocs are readily floated with rising rates in the order of 120 mh-1, values higher than those obtained for the settling of the non-aerated flocs (18 - 24 mh-1). The FGR requires short residence times and generates dense, well structured flocs (with a mass fractal dimension, dF of about three) which withstand high shear forces. Mechanisms involved appear to include small bubble formation and their rapid occlusion (entrapment) within flocs, nucleation of bubbles at floc/water interfaces, polymer coiling as a result of æsalting outÆ effects at the aqueous/air interface and plug flow type of mixing (flocculation). Successful examples of emulsified oil and solids removal from water are shown and because in all cases high efficiencies were obtained (>90 per cent removal). Due to the high process efficiency and high loading capacity shown, the FGR appears to have good potential as an in-line flotation-separator device in applications requiring high rate solid-liquid or liquid-liquid separations.

Jan 1, 2005

By Norman O. Lotter, André R. Laplante

"The pursuit of concentrator surveying for purposes of metal accounting or process optimization has not yet connected with the well-published realm of geostatistics. The reality of lognormality in time has seldom been discussed. One publication by Krige, 1962, examined such effects for a gold concentrator in South Africa, towards an information system that would provide feedback to the mining and surveying teams on grade control of ore mined.During present studies which are designing and testing a new survey model, called statistical benchmark surveying, it was found that the distributions of feed, concentrate and tailings bear significant residual signs of the parent lognormality in space. The multiple hosting of paymetals in different mineral species complicates the understanding of these distributions. These features have to be recognized and treated in order to perform appropriate quality control on the diagnostic sampling performed in the pursuit of statistical benchmark surveying.It is shown in this paper that the above two features can actually be used to advantage in the diagnosis of continuous periods of operations data ahead of such surveying, including the estimation of recoverable paymetals in flotation tailings from a graphical method.INTRODUCTIONAssessment of Concentrator PerformanceMilling and flotation, sometimes accompanied by gravity separation, are well-established unit processes, which have traditionally been used to treat ore that has been mined. This is because these processes liberate, then separate, the valuable minerals, which contain paymetals, from host gangue. This is often done by a combination of crushing and grinding processes, or autogenous grinding, to liberate the paymetal minerals, followed by gravity separation and/or flotation, to separate these valuable minerals into a concentrate, or several concentrates. These concentrate(s) have a lower bulk than the parent ore from which they are derived. Further, they contain a high percentage of the valuable minerals. Accordingly, they are more economically treated in subsequent beneficiation processes than the ore from which they were produced."

Jan 1, 2005

By T. A. Utigard

To improve recoveries of Ni, Cu and Co in the Inco flash furnace, a new operating concept was investigated. By adding sufficient coke to form a supernatant coke layer, a reducing barrier would form allowing for improved reduction of descending oxidized sulfide mineral particles formed in the flame. The objective of this investigation was to study the kinetic mechanism and efficiency of the coke layer to produce a sulfur deficient matte. The mechanism and rate of carbon reduction of each of the phases formed in the flash flame, i.e. sulfides and oxysulfides were investigated by means of X-ray visualization tests. Graphite-slag reduction was also conducted for comparison purposes. In the case of slag, poor wettability and the formation of a gas film on the surface of the carbon reductant are often blamed for limiting the reaction surface area that ultimately results in poor reaction kinetics. The X-ray visualization tests confirmed that matte and oxysulfide wet coke better than slag and that the rates of reduction of matte and oxysulfide are faster than that of slag.

Jan 1, 2005

By George J. Karcas, Raimo Kuusisto, Pertti Pekkala

Ongoing Outokumpu development in Solvent Extraction and Electrowinning Technology, involving all aspects of process chemistry, equipment and control, extends over a period of close to 30 years. The development in SX started with molybdenum and rhenium, continued with zinc, manganese, cobalt and nickel and is now focusing on copper. The OutoCompact VSF? SX concept, which has been recently introduced, is a honed version of earlier VSF? technology. The Outokumpu VSF? ("Vertical Smooth Flow") SX package includes the DOP ("Dispersion Overflow Pump") units, the Spirok Mixers, the OutoCompact Settlers including their DDG ("Dispersion Depletor Gate") fences and tank farm equipment such as the LOS ("Loaded Organic Scrubbing") tank as well as the CEP ("Copper Electrolyte Purifying") tank. Although the VSF? SX package can be implemented according to several optional lay-outs, the so-called Track version has lately been introduced to the advantage of new plants. The new OutoCompact SX technology decreases the footprint of future VSF? plants. The lay-out, including plant size flexibility, have further been improved by Outokumpu?s new OutoReverse settler technology. Two of several SX plants currently under construction rely on reverse settlers in order to maximize their performance. The Outokumpu EW technology includes process know-how as well as proprietary equipment. The copper EW package consists of permanent stainless steel cathodes based on wax-less technology and lead anodes utilising polymer concrete cells with the double contact bus bar system and ventilation hoods fitted for efficient mist control. The lifting of cell hoods, as well as cathode washing, is done by the cathode pulling crane. Proper electrolyte flows and matching current density further ensure high productivity of LME grade copper cathodes.

Jan 1, 2005

By S Bluhm, R Funnell

Creative mine-designs are constantly being applied in the deep platinum mining industry in South Africa. Recently, this has resulted in deep hot mine-designs including room and pillar, bord and pillar or stall and pillar layouts and the use of in-stope trackless mechanisation. In these mines, the ventilation systems use refrigerated air and high fan pressures and as a result ventilation leakage can have a huge impact. Leakage is a serious impediment to cost-effective operation and potential leakage in future projects is a major factor in judging project viability. This paper describes certain mine layouts and quantifies the extent of the leakage. Based on typical field data, a range of seals from ævery poorÆ to ævery goodÆ was defined and used to estimate overall leakage. Within these mine networks the ventilation pressure, temperature and density all vary significantly and with the multiplicity of leakage paths it was necessary to make use of the VUMA-network simulation package. For the examples examined, the leakage was found to be up to 85 per cent for æpoorÆ category seals and up to 50 per cent for ægoodÆ category seals. The total air flow (and refrigeration) requirements grow exponentially with strike distance due to the compounding effects of higher pressure and more leakage paths. It is shown that beyond certain depths and strike distances the leakage will become so great that it will be impossible to operate cost-effectively û even with ægoodÆ seals. Indeed, in these examples the projects were not considered viable in their original format because of the high ventilation-cooling costs and the mine-designs were modified to include footwall drive systems û the cost of which was justified by the reduced strategic risk to operating ineffectiveness due to leakage.

Jan 1, 2005

By Roberto J. Guardia, Ted Lewtas, Peter Rasmussen, Klaus Winkler

As part of the Lake Fort Smith Water Supply Dam Enlargement project, located in northwest Arkansas, microtunneling methods were used to install two side-by-side,1.53m (60-in) inside-diameter steel pipes between the intake structure shaft and the lake. The 46.6 m- (153 ft-) and 41.7 m- (137 ft-) long tunnels were excavated in Pennsylvanian sedimentary bedrock ranging from coarse sandstone to siltstone and shale-like claystone. The intake tunnels were constructed 18.3 m (60 ft) below lake level from the dry shaft. Special installation methods and procedures described herein were used to complete the lake taps. Installation difficulties that caused minor delays are also reviewed. After the excavation of the Intake shaft was completed, the two lake taps were installed in approximately ten weeks with the same microtunneling machine.

Jan 1, 2005

By B. Xu

Keywords: Magnetic damping, g-jitter, Hot-film anemometry Results from an experimental study on natural convection induced by temperature gradient in molten gallium contained inside a rectangular container. The damping effect of the convective flow from an externally applied static magnetic field is investigated. Induced velocity and temperature fields are mapped using a standard constant temperature hot-film anemometry and a thermocouple with and without the applied magnetic field, respectively. Detailed experimental setup and procedure are depicted in the present paper. Obtained velocity and temperature profiles are examined against previous numerical simulations and reasonably good agreement has been achieved. Obvious damping effect can be observed in both the temperature and the velocity profiles when the external magnetic field presents.

Jan 1, 2005

By Kim Fagerlund

Boliden Harjavalta Oy operates a copper smelter in Finland, which is based on flash smelting together with Peirce-Smith converting of copper matte. This paper reviews a case study when a high arsenic feed mixture was successfully eliminated in order to guarantee the anode quality. Based on theoretical and practical knowledge in slag chemistry at Outokumpu Research, the CaO-fluxing practice was introduced. Description of a thermodynamic simulation using MTDATA and implementation of the results into converting practice is given. Results showed that the impurity fluctuations in raw materials could be effectively controlled by efficient utilization of different slag chemistry.

Jan 1, 2005

By A. Kepeski

Cement industry relies heavily on the control of large volume of raw materials in the proximity of plant operations for clinker and cement manufacturing. These mineral resources are perhaps considered as ?low-profile? (mostly comprise limestone's, clays, marls and sands), but their availability, accessibility and suitability ? the later with respect to chemistry, mineralogical and physical characters ? are factors of paramount importance and may largely affect production cost and plant productivity. The combination of scarcity of good quality raw materials deposits and the growing environmental concerns have challenged the cement producers towards sustainability and the responsible exploitation of natural resources. In open pit mining and quarrying, the evaluation of mineral resources vs. handling of the non-usable overburden and other off-spec materials directly affects the medium to long-term production planning, quality control practices and environmental management. It is a general trend for many cement producers and a usual case for a number of Titan Cement plants worldwide, that redesign of quarry pits is necessary not only for stability purposes but also as a result of environmental constraints and emerging issues. The material reserves then have to be re-evaluated in the light of the new final pit design, safety distances from houses, other infrastructure and Law restrictions and according to criteria of safety of operations, reduction of environmental impacts, pit optimisation and proper future reclamation. The paper discusses the case of three active quarries of Usje Cement Plant, in Skopje (Macedonia), namely Usje (marl), Goverlevo (lime-stone) and Ljubosh (sand), where a large campaign of redesign and evaluation of recoverable reserves and the needs in rehabilitation took place in 2004. Technical and environmental issues and criteria are presented in the form of master plans and the highlights of the first attempts to propose and apply a reclamation scheme are discussed, by also examining alternative solutions for each quarry area. Finally, the 2005 progress in applying changes to the design of benches and pit layout, as well as experiences gained, are discussed.

Jan 1, 2005

By F. M. C. C. Vieira

The DEEPMINE Research Programme sought to develop the technology and competence to mine gold safely and profitably at depths of 3 to 5 km. Among the many issues addressed was the stability and support of rockpasses at ultra-depth. It was found that high virgin and mining-induced stresses could cause the walls of rockpasses to spall, leading to the deterioration and failure. A comprehensive programme of numerical modelling was conducted to investigate alternative mining layouts and sequences to ameliorate the problem.

Jan 1, 2005

By A Winchester, D Grant

The massive 1100 Orebody in Mount IsaÆs X41 Copper Mine has been extracted over the last 40 years form north to south utilising sublevel open stoping methods.De velopment has continually stepped ahead of production to provide access to new primary stoping blocks. The remaining secondary pillars contain stopes with one, two or three fill mass exposures and were constrained by access requirements and stope extraction turnaround time.The remaining southern mining areas consist of large 40 m wide by 300 to 400 m long east-west transverse pillars that have been left to provide access for ventilation and service requirements. Three large transverse cross-cuts or transverse pillars û 4180 x/c, 4010 x/c and the Panel pillar now remain. The 4180 x/c was the last major transverse pillar to be successfully broken.This transverse pillar is being extracted in a retreating sequence, creating 3SLOS stopes due to the surrounding backfilled stopes.In recent years the extraction of the first, and most critical, stopes in the transverse pillars have resulted in large changes to the induced stress field. This paper describes the extraction of the 1.1 million tonne stope P418 in the 4180 x/c pillar.T echnical challenges that were faced and how they were overcome to allow for the successful extraction of the stope are described.Critical to the success of the P418 stope extraction were the rehabilitation methodology used; extraction strategy modifications to address deteriorating ground; mass firings with multiple directional changes; managing the exposure of backfill of variable strengths; and geotechnical monitoring prior to, during and after extraction.

Jan 1, 2005

By Narendra N. Khatri, Michael Deutscher, Jozef F. Zurawski

Five sewer connections were required to divert Combined Sewer Overflow (CSO)from existing outfalls to an old underutilized large diameter brick sewer (the Easterly Interceptor). The connections were part of an on-going CSO control program by the Northeast Ohio Regional Sewer District (NEORSD) in the City of Cleveland, Ohio. Each connection was made by pipejacking and hand-mining a fiberglass-reinforced polymer (FRP) pipe through soft glaciolacustrine clays and silts. Jet grouting was utilized to stabilize the soils and fill the voids surrounding the interceptor prior to making the underground connection. Reinforced concrete liners were constructed inside the aging brick sewer to provide structural stability during ground improvements and connection work. The project also involved micro tunneling two approximately400 foot lengths of FRP pipe through soft ground using a slurry pressure balanced machine.

Jan 1, 2005

This paper addresses, in particular, the influence of winding depth on the selection of head ropes for Koepe winders. Because this is just one aspect of winder design that affects the operational safety of the winding system, the paper starts by considering all the issues governing the life and safety of the winding ropes. Regulations from a variety of countries are reviewed and comparisons of the legislated rope factors of safety and their variation with winding depth are made. This is followed by a discussion of the typical observed mode of in-service deterioration of Koepe head ropes. This mode of deterioration is due to fatigue and is influenced by the load range occurring in the ropes. Parameters contributing to load range are discussed and the influence of winding depth is highlighted. Lessons learned from early experience with very deep Koepe winders in South Africa are recalled. Predictions of load range as a function of depth are made, from which general rope life predictions are made for ropes selected by conventional national factor of safety requirements. This is illustrated in graphs comparing rope life as a function of depth. Typically a reducing life with depth is predicted. A rope selection strategy is advocated, which is based on achieving a constant rope life irrespective of the depth of wind. A new factor of safety (or rope design factor) equation is prepared that has the trend of increasing with depth. This proposed equation is compared with other published proposals that promote an increasing rope factor of safety with depth. It is shown that smoother winder drive controls enhance winding rope life and this improvement is quantified. The paper concludes by pointing out the consistency in predicted and observed life of winding ropes selected in accordance with legislated factor of safety approaches. It recommends the adoption of a new rope design factor equation for rope selection, to be used in conjunction with appropriate codes of practice for winding rope condition assessment and for the design, installation, operation, maintenance and testing of Koepe winders. The new rope design factor equation approaches a limiting economic depth of wind at shallower depths than the existing Koepe factor of safety approaches. However these older approaches æbuild-inÆ a reducing rope life with depth. The new rope design factor is therefore a more consistent way to select Koepe ropes and to evaluate economic trade-offs between Koepe and conventional double-drum or Blair winding systems.

Jan 1, 2005

By Raymond A. Binns

Exploration for undersea polymetallic sulfide mineral resources with high economic potential would be more effective given an ability to predict sites with particularly high gold contents (averaging say > 10 ppm Au). Herzig et al (1993) addressed this issue shortly after recognition that deposits in the back-arc Lau Basin (average 3.8 ppm Au) were enriched in gold relative to mid-ocean ridge sites (average 1.2 ppm Au). Small but significant numbers of hydrothermal sites with massive sulfide deposits averaging >10 ppm Au have since been discovered. The principal genetic factors underlying gold enrichment include depositional processes at and below the seabed, and the source of gold. It is timely to consider whether resolution of their relative importance can be translated into practical criteria for exploration strategies focused on especially gold-rich deposits. Comparing the ?grade? of seafloor deposits using analyses cited in research papers is fraught with difficulty, but there is no alternative at present to assuming that such averages provide an initial tenor guide. On this basis, four known polymetallic hydrothermal sites from convergent plate margins fit the exceptional-gold category with >10 ppm ?average? Au, while one from a divergent margin comes close: Sunrise (Myojin Knolls; 20 ppm ?average? Au) and Suiyo Seamount (28 ppm Au) in the Izu-Bonin Arc are frontal arc volcanoes dominated by rhyolite and dacite respectively, contrasting with more common mafic neighbor edifices (Iizasa et al., 1999). In both cases gold-rich massive sulfides occur in summit calderas with significant development of pumiceous volcaniclastic rocks, at depths around 1300 and 1370 m respectively. In the Eastern Manus Basin, PACMANUS (~1700 m; 14 ppm Au) and Suzette (~1550 m; 22 ppm Au) occur along the crests of volcanic ridges dominated by dacite/rhyodacite and andesite/mafic dacite respectively (Binns, 2004). Caldera structures are lacking. Although the Eastern Manus Basin is tectonically a rifted back-arc, its submarine volcanic edifices (picritic basalt to rhyodacite) have distinctly arc-style geochemical and isotopic affinities, differing from more typical back-arc basin basalts at the spreading axis further west (central Manus Basin). Probably as a consequence of transpression and a marked rupture in the New Britain subduction zone, submarine arc volcanism has here extended into the rifted back-arc region.

Jan 1, 2005

By Huang Kai

By adding the solid oxalate acid powder into the solution of nickel chloride or its ammonia coordinated solution, the uniform compound particles were prepared and the precipitated particles were transferred to the mono-dispersed NiO particles by calcination. In this study, the various experimental conditions were investigated, the characteristics of the corresponding obtained particles were analyzed, and the formation mechanism of the particles was elucidated. It was found that the solid oxalate acid provided the solid-solution interface for the precipitation and induced the nucleation and growth of the product particles.

Jan 1, 2005