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94-560: The Bushveld Igneous Complex and some other similar intrusions formed during this period. The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period. For the time interval from 2250 Ma to 2060 Ma, an alternative period based on stratigraphy rather than chronometry, named either the Jatulian or the Eukaryian ,

188-510: A Johnson Matthey 2013 estimate. The demand of platinum has somewhat steadily been increasing, driven by the more intensive use per capita with developing area and urbanization, the demand reached an all-time high in 2005 of 208.3 metric tons. From 1975 to 2013, the autocatalytic and jewellery industry dominated the market with more than 70% of the gross demand. Jewellery was barely ahead of autocatalysts prior to 2002 with brute gross demand values being somewhat similar or higher. From 2002 to 2003,

282-423: A crystal at a high speed, sweeping away nuclei that would otherwise be incorporated into a crystal, causing the swept-away nuclei to become new crystals. Contact nucleation has been found to be the most effective and common method for nucleation. The benefits include the following: The following model, although somewhat simplified, is often used to model secondary nucleation: where Once the first small crystal,

376-428: A draft tube while outside the crystallizer there is a settling area in an annulus; in it the exhaust solution moves upwards at a very low velocity, so that large crystals settle – and return to the main circulation – while only the fines, below a given grain size are extracted and eventually destroyed by increasing or decreasing temperature, thus creating additional supersaturation. A quasi-perfect control of all parameters

470-538: A focus on PGEs (primarily platinum and palladium), vanadium, iron (generally from magnetite), chromium, uranium, tin, ... There are multiple major mining companies that are heavily involved within this area, particularly AngloAmerican , African Rainbow Minerals , Impala Platinum , Northam Platinum Ltd. , Lonmin plc , and more recently Bushveld Minerals . It has been reported that more than 20 billion metric tons of PGE ore rock has been indicated in South Africa by

564-421: A function of operating conditions with a fairly complicated mathematical process called population balance theory (using population balance equations ). Some of the important factors influencing solubility are: So one may identify two main families of crystallization processes: This division is not really clear-cut, since hybrid systems exist, where cooling is performed through evaporation , thus obtaining at

658-407: A jacket around the trough. Crystals precipitate on the cold surfaces of the screw/discs, from which they are removed by scrapers and settle on the bottom of the trough. The screw, if provided, pushes the slurry towards a discharge port. A common practice is to cool the solutions by flash evaporation: when a liquid at a given T 0 temperature is transferred in a chamber at a pressure P 1 such that

752-414: A major impact on the size, number, and shape of crystals produced. As mentioned above, a crystal is formed following a well-defined pattern, or structure, dictated by forces acting at the molecular level. As a consequence, during its formation process the crystal is in an environment where the solute concentration reaches a certain critical value, before changing status. Solid formation, impossible below

846-617: A non-exhaustive list: The three largest ore bodies are the Merensky Reef , the UG2 Chromitite Reef and the Platreef : * Table modified from USGS , 2010. Most of the identified mineral inventory is from the three described reefs, most of it is located within the eastern limb but most of the reserves are found within the western limb. The chrome deposits of the Bushveld forms

940-419: A relatively variable quality of the product along with the batch. The Swenson-Walker crystallizer is a model, specifically conceived by Swenson Co. around 1920, having a semicylindric horizontal hollow trough in which a hollow screw conveyor or some hollow discs, in which a refrigerating fluid is circulated, plunge during rotation on a longitudinal axis. The refrigerating fluid is sometimes also circulated in

1034-416: A second solvent to reduce the solubility of the solute (technique known as antisolvent or drown-out), solvent layering, sublimation, changing the cation or anion, as well as other methods. The formation of a supersaturated solution does not guarantee crystal formation, and often a seed crystal or scratching the glass is required to form nucleation sites. A typical laboratory technique for crystal formation

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1128-461: A significant impact on the global environment. The environmental costs for platinum mines are only slightly higher in energy, somewhat lower in water and moderately higher in greenhouse gas emissions when compared to gold mining. South Africa's economy is heavily tied to its mining industry and has been greatly affected by low metal prices. Mining companies have had to cut costs by lowering production, closing mines, selling off projects, and reducing

1222-546: A solution than small crystals. Also, larger crystals have a smaller surface area to volume ratio, leading to a higher purity. This higher purity is due to less retention of mother liquor which contains impurities, and a smaller loss of yield when the crystals are washed to remove the mother liquor. In special cases, for example during drug manufacturing in the pharmaceutical industry, small crystal sizes are often desired to improve drug dissolution rate and bio-availability. The theoretical crystal size distribution can be estimated as

1316-507: A transformation to the equilibrium phase. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature, such as in

1410-490: Is nucleation , the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth , which is the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface and lodge themselves into open inconsistencies such as pores, cracks, etc. The majority of minerals and organic molecules crystallize easily, and

1504-453: Is a consequence of the physical characteristics of the solution, while the others define a difference between a well- and poorly designed crystallizer. The appearance and size range of a crystalline product is extremely important in crystallization. If further processing of the crystals is desired, large crystals with uniform size are important for washing, filtering, transportation, and storage, because large crystals are easier to filter out of

1598-475: Is a norite with extensive chromitite and sulfide layers or zones containing the ore. The Reef contains an average of 10 ppm platinum group metals in pyrrhotite , pentlandite , and pyrite as well as in rare platinum group minerals and alloys . The Merensky and UG2 reefs contain approximately 90% of the world's known PGM reserves. About 80% of the platinum and 20% of the palladium mined each year are produced from these horizons. The formation mechanisms of

1692-520: Is also quarried from parts of the complex and rendered into dimension stone . There have been more than 20 mine operations. There have been studies of potential uranium deposits. The complex is well known for its chromitite reef deposits, particularly the Merensky reef and the UG2 reef. It represents about 75 percent of the world's platinum and about 50 percent of the world's palladium resources. In this respect,

1786-539: Is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering , crystallization occurs in a crystallizer . Crystallization is therefore related to precipitation , although the result is not amorphous or disordered, but a crystal. The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. Nucleation

1880-403: Is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure – note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure. The crystal growth

1974-415: Is clear that sulfate solubility quickly decreases below 32.5 °C. Assuming a saturated solution at 30 °C, by cooling it to 0 °C (note that this is possible thanks to the freezing-point depression ), the precipitation of a mass of sulfate occurs corresponding to the change in solubility from 29% (equilibrium value at 30 °C) to approximately 4.5% (at 0 °C) – actually a larger crystal mass

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2068-754: Is defined by the Melinda Fault, which dips to the west and is situated within the Pietersburg terrane. The Melinda Fault extends in an eastern direction along the Palala Shear Zone (PSZ). This Fault and the PSZ are collectively designated as the Palala-Zoetfontein Lineament. The TML represents the boundary between the southern portion of the Northern Limb and the remainder of the Bushveld. It demarcates

2162-636: Is displaced 500 m to the south by the Makweng Fault. The Sekhukhune Fault trends in a north-south direction and has a throw of up to 2 km to the west. The Sekhukhune Fault is situated to the east of the Fortdraai Anticline. The Laersdrift Fault is located to the NW of the eastern Bushveld Complex. The Pilanesberg Complex is situated in the western lobe of the Bushveld Complex. The southern part of

2256-411: Is facing a lack of education, high crime levels, and health problems within the workforce. Additionally, they are facing high poverty levels, government deficits, and are still heavily dependent on the platinum mining industry which is "responsible for more than 65% of local GDP and 50% of all direct jobs" (over 70,000 jobs). The accommodations and housing are lacking and have seen little to no effort from

2350-423: Is increased using the technique of evaporation . This process is insensitive to change in temperature (as long as hydration state remains unchanged). All considerations on control of crystallization parameters are the same as for the cooling models. Most industrial crystallizers are of the evaporative type, such as the very large sodium chloride and sucrose units, whose production accounts for more than 50% of

2444-542: Is precipitated, since sulfate entrains hydration water, and this has the side effect of increasing the final concentration. There are limitations in the use of cooling crystallization: The simplest cooling crystallizers are tanks provided with a mixer for internal circulation, where temperature decrease is obtained by heat exchange with an intermediate fluid circulating in a jacket. These simple machines are used in batch processes, as in processing of pharmaceuticals and are prone to scaling. Batch processes normally provide

2538-580: Is separated from the others by structural boundaries. The southern and central zones are separated by the Steelpoort Fault. The eastern lobe is further subdivided by the presence of the Stofpoort and Wonderkop Faults, which serve to differentiate the northeast from the central zone. The Stofpoort Fault is situated in close proximity to the Olifants River. The western zone is separated from the remainder of

2632-493: Is the initiation of a phase change in a small region, such as the formation of a solid crystal from a liquid solution. It is a consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium. Total nucleation is the sum effect of two categories of nucleation – primary and secondary. Primary nucleation is the initial formation of a crystal where there are no other crystals present or where, if there are crystals present in

2726-505: Is the process by which solids form, where the atoms or molecules are highly organized into a structure known as a crystal . Some ways by which crystals form are precipitating from a solution , freezing , or more rarely deposition directly from a gas . Attributes of the resulting crystal depend largely on factors such as temperature , air pressure , cooling rate, and in the case of liquid crystals , time of fluid evaporation . Crystallization occurs in two major steps. The first

2820-476: Is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors ( temperature , supersaturation , etc.). It

2914-415: Is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by K sp . Depending upon

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3008-414: Is to dissolve the solid in a solution in which it is partially soluble, usually at high temperatures to obtain supersaturation. The hot mixture is then filtered to remove any insoluble impurities. The filtrate is allowed to slowly cool. Crystals that form are then filtered and washed with a solvent in which they are not soluble, but is miscible with the mother liquor . The process is then repeated to increase

3102-564: Is to perform a gravity settling to be able to extract (and possibly recycle separately) the (almost) clear liquid, while managing the mass flow around the crystallizer to obtain a precise slurry density elsewhere. A typical example is the DTB ( Draft Tube and Baffle ) crystallizer, an idea of Richard Chisum Bennett (a Swenson engineer and later President of Swenson) at the end of the 1950s. The DTB crystallizer (see images) has an internal circulator, typically an axial flow mixer – yellow – pushing upwards in

3196-430: The 2014 South African platinum strike . Platinum is more likely to be affected by social, environmental, political and economic issues where as gold not as much. This is because platinum has large mineral resources already identified and is not expected to be depleted for many decades (potentially up to year 2040). Furthermore, platinum is geographically restricted to the three by far the most significant resources, namely

3290-546: The Platinum Group Elements (PGEs) and Platinum Group Metals (PGMs), chromium , copper , nickel , gold and vanadium concentrates, reef formation and orientation , and affect the type of mineralization, for example magmatic and hydrothermal deposits . Tectonic controls and effects can be seen or indicated by stratigraphic and crustal thickening and thinning, record of tectonic activity by type of structure such as collision and rifting , and influence on

3384-560: The Steelpoort Shear Zone (SSZ). These shear structures control several factors and have major geological implications within the Bushveld Igneous Complex, including structural, mineralogical , tectonic , metamorphic and economic . Some structural controls include the direction and flow of magma and intrusions , structural traps for mineralization and the structural evolution of the complex. Mineralization controls

3478-419: The entropy ( S ) gain in the system by spatial randomization of the molecules has overcome the enthalpy ( H ) loss due to breaking the crystal packing forces: Regarding crystals, there are no exceptions to this rule. Similarly, when the molten crystal is cooled, the molecules will return to their crystalline form once the temperature falls beyond the turning point. This is because the thermal randomization of

3572-711: The outcrops around what appears to be the edge of a great geological basin : the Transvaal Basin . It is approximately two billion years old and is divided into four limbs: northern, eastern, southern and western. It comprises the Rustenburg Layered suite, the Lebowa Granites and the Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first publicised around 1897 by Gustaaf Molengraaff who found

3666-501: The sexual reproduction found within the eukaryotes only, thus the alternative name Eukaryian. Macroscopic life is discovered to have started during the Rhyacian period. This geochronology article is a stub . You can help Misplaced Pages by expanding it . Bushveld Igneous Complex The Bushveld Igneous Complex ( BIC ) is the largest layered igneous intrusion within the Earth's crust . It has been tilted and eroded forming

3760-401: The solubility threshold at the given temperature and pressure conditions, may then take place at a concentration higher than the theoretical solubility level. The difference between the actual value of the solute concentration at the crystallization limit and the theoretical (static) solubility threshold is called supersaturation and is a fundamental factor in crystallization. Nucleation

3854-716: The BIC, the great dyke (Zimbabwe) and Noril'sk-Talnakh in Russia. An important detail to note is that palladium has been and is considered as the alternative to platinum. Recently (2017), the supply-demand gap has greatly decreased. Looking at political and social issues, there have been quite a few platinum mining-related strikes since before the 21st century: Impala strike, 1986 Gencor strike, 2004 Impala and Anglo Plats strikes, 2007 South Africa miners' strike , 2012 Marikana killings , Lonmin 2013 strike, and 2014 South African platinum strike . Crystallisation Crystallization

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3948-403: The Bushveld Complex still remains as one of the prime sources of PGE ore. There have been many strikes for unfair pay and working conditions, illegal miners (so-called " zama-zamas "), gun-fire conflicts , political swindles and legal fights. The prime use of platinum is for auto-catalytic converters (in cars) and jewellery. The total net demand of PGE in 2012 was 197.4 metric tons according to

4042-475: The Bushveld complex is unique and one of the most economically significant mineral deposit complexes in the world. The Bushveld Igneous Complex covers a pear-shaped area in the central Transvaal . It is divided into an eastern and western lobe, with a further northern extension. All three sections of the system were formed around the same time—about 2 billion years ago—and are remarkably similar. Vast quantities of molten rock from Earth's mantle were brought to

4136-558: The Bushveld igneous complex. Similarly, another study has found high concentrations of microscopic (<63 μm) PGE airborne dust particles near the mining areas. These have been found to be transported surface runoff and atmospherically, then further concentrated into soils and rivers such as the Hex River which flows directly into Rustenburg, the most populated municipality of North West Province of South Africa. A study from Maboeta et al. in 2006, has revealed through chemical analysis that

4230-690: The Jagersfontein, Klerksdorp and Potgietersrus shear zones and the Thabazimbi-Murchison lineament, chromium with the Rustenburg Layered Suites (RLS) critical zone and the TML, and gold with the Jagersfontein and Klerksdorp shear zones. Vanadium deposits are associated with the vanadium-rich magnetite deposits of the Bushveld, such as the TML, some of which may be associated with shear zones, and copper and nickel deposits, which often occur together in

4324-605: The PSZ is located in the northern part of the BIC, trends EW and can be 5–10 km wide. Two distinct fault orientations have been identified within the Pietersburg terrane: a NE–SW orientation and an ENE–WSW orientation. The most conspicuous faults with these orientations are the YPF and the Zebediela Faults. Different mineral occurrences are more strongly associated in the BIC in specific shear zones. PGEs are generally associated with

4418-663: The Pilanesberg Complex exhibits NW–SE isopach lines that trend parallel to the Rustenburg Fault, which dips in the same direction towards the center of the Western Bushveld Complex. The Brits Graben is situated in the eastern region, in close proximity to Hartebeespoort . This Graben is delimited by a series of parallel faults, among which the most prominent is the Brits Fault, which trends NW–SE and intersects

4512-673: The Rustenburg Layered Suite, the Transvaal Supergroup and the Pretoria Group. The BSZ is NW–SE trending and is located within the Brits Fault. The NE–SW trending Ysterberg–Planknek Fault (YPF) is situated within the northern lobe of the Bushveld Complex. An additional ENE–WSW trending fault is situated within the northern lobe and is designated the Grasvally Fault. The boundary between the northern and southern lobes

4606-542: The UG2 chomitites is dominated by granular orthopyroxene, interstitial plagioclase and clinopyroxene with minor variable amounts accessory minerals such as phlogopite. The UG2 chromitites are underlain by pyroxenite footwall that is distinct from hanging wall pyroxenite. Chromite subhedral to subrounded (less than 0.5 mm in size) grains are a minor (c. 4%) but constant phase that is embedded with orthopyroxene (and other interstitial phases such as mentioned) throughout this footwall pyroxenite. Large oikocrysts are visible within

4700-581: The boundary between the Pietersburg terrane and the central portion of the Kaapvaal Craton . In general, the TML is a large EW trending shear zone that forms a boundary between the Bushveld Complex and the Limpopo Belt and is 20 and 30 km wide. The JSZ is located within the TML, it trends NE–SW and is between 10 and 15 km wide. The KSZ runs parallel to the JSZ, trends NS and can be up to 10 km thick in places, while

4794-574: The chromitite seams in the Bushveld Igneous Complex are highly debated: numerous mechanisms have been proposed. The following is a non-exhaustive list of chromitite formations process. There has been a proposal of the origins of at least three different processes used to model the PGE mineralization in the area: The Bushveld Igneous Complex is a layered mafic intrusion (LMI) with well-defined ore bodies of stratiform chromitite layers concentrated with

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4888-469: The conditions are favorable, crystal formation results from simply cooling the solution. Here cooling is a relative term: austenite crystals in a steel form well above 1000 °C. An example of this crystallization process is the production of Glauber's salt , a crystalline form of sodium sulfate . In the diagram, where equilibrium temperature is on the x-axis and equilibrium concentration (as mass percent of solute in saturated solution) in y-axis , it

4982-409: The conditions, either nucleation or growth may be predominant over the other, dictating crystal size. Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism . Certain polymorphs may be metastable , meaning that although it is not in thermodynamic equilibrium , it is kinetically stable and requires some input of energy to initiate

5076-668: The different exploration and mining companies of which contains about 38.1 kilotons of platinum metal in mineral reserves and resources in the Bushveld. The sum of PGEs and Gold resources and reserves equates to a total of about 72 kilotons from the Bushveld Complex alone. Most are underground mines (such as Longhole Stoping, Drift-and-Fill mining, etc. ), fewer are open pit like the large Mogalakwena mine . Mining feasibility studies have identified impacts on surface water , groundwater , wetlands , flora , fauna and related social issues. Additionally, these impacts include increased drainage of salts, sediments thought channels and streams near

5170-706: The earliest phase of the Complex. The Complex includes layered mafic intrusions (the Rustenburg Layered Suite) and a felsic phase. The complex has its geographic centre located north of Pretoria in South Africa at about 25° S and 29° E . It covers over 66,000 km (25,000 sq mi), an area the size of Ireland . The complex varies in thickness, in places reaching 9 kilometres (5.6 mi) thick. Lithologies vary from largely ultramafic peridotite , chromitite , harzburgite , and bronzitite in

5264-464: The evolution of the BIC. Metamorphic controls are localised metamorphism and alteration in shear zones, they affect mineral formation and stability, and they may show evidence of pressure - temperature - time (P-T-T) paths. Economic controls include, mineral deposits, they help to guide mining and exploration and with resource and reserve estimation and extraction. The eastern lobe of the Bushveld Complex comprises three distinct zones, each of which

5358-456: The exchange surfaces. The Oslo, mentioned above, is a refining of the evaporative forced circulation crystallizer, now equipped with a large crystals settling zone to increase the retention time (usually low in the FC) and to roughly separate heavy slurry zones from clear liquid. Evaporative crystallizers tend to yield larger average crystal size and narrows the crystal size distribution curve. Whichever

5452-444: The form of PGE-Chloride in the liver, kidneys, bones and lungs. The intake is generally through metallic or oxide dust that is inhaled or is absorbed through the skin causing contact dermatitis , on the long term causing sensitization and can eventually to lead to cancers. A study from January 2013, has shown an increasing trend of the development of silicosis caused by silica dust and asbestos fibers related to workers mining in

5546-405: The form of the crystallizer, to achieve an effective process control it is important to control the retention time and the crystal mass, to obtain the optimum conditions in terms of crystal specific surface and the fastest possible growth. This is achieved by a separation – to put it simply – of the crystals from the liquid mass, in order to manage the two flows in a different way. The practical way

5640-480: The formation of a structure rather like a layered cake consisting of distinct rock strata, including three PGM-bearing layers, referred to as reefs. Large portions of the central area are covered by younger rocks. The extrusions were emplaced over an early diabasic sill, outcrops of which are visible on the southeastern side of the Complex. These are typically greenish in colour and composed of clinopyroxene , altered to hornblende and plagioclase , and are regarded as

5734-399: The gross demand significantly decreased in jewellery (87.7 to 78.1 tons), but has largely increased in autocatalysts (80.6 to 101.7 tons) and has since then almost consistently dominated the market (with 2009 being the one exception linked to weak car sales). In 2016, the platinum market continued to be in deficit for the 5th consecutive year, just barely reaching a demand 200,000 oz. In 2017,

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5828-457: The growing crystal. The supersaturated solute mass the original nucleus may capture in a time unit is called the growth rate expressed in kg/(m *h), and is a constant specific to the process. Growth rate is influenced by several physical factors, such as surface tension of solution, pressure , temperature , relative crystal velocity in the solution, Reynolds number , and so forth. The main values to control are therefore: The first value

5922-476: The influence of the existing microscopic crystals in the magma. More simply put, secondary nucleation is when crystal growth is initiated with contact of other existing crystals or "seeds". The first type of known secondary crystallization is attributable to fluid shear, the other due to collisions between already existing crystals with either a solid surface of the crystallizer or with other crystals themselves. Fluid-shear nucleation occurs when liquid travels across

6016-416: The last crystallization stage downstream of vacuum pans, prior to centrifugation. The massecuite enters the crystallizers at the top, and cooling water is pumped through pipes in counterflow. Another option is to obtain, at an approximately constant temperature, the precipitation of the crystals by increasing the solute concentration above the solubility threshold. To obtain this, the solute/solvent mass ratio

6110-410: The liquid saturation temperature T 1 at P 1 is lower than T 0 , the liquid will release heat according to the temperature difference and a quantity of solvent, whose total latent heat of vaporization equals the difference in enthalpy . In simple words, the liquid is cooled by evaporating a part of it. In the sugar industry, vertical cooling crystallizers are used to exhaust the molasses in

6204-482: The lower sections to mafic norite , anorthosite , and gabbro toward the top, and the mafic Rustenburg Layered Suite is followed by a felsic phase (the Lebowa Granite Suite). The orebodies within the complex include the UG2 (Upper Group 2) reef containing up to 43.5% chromite , and the platinum-bearing horizons Merensky Reef and Platreef . The Merensky Reef varies from 30 to 90 cm in thickness. It

6298-542: The majority in terms of the proportion of all the known chrome reserves of the world. This area is very strategic as it is easy and cheap for mining; this is because their continuity in thick seams over scores of miles of strike and their persistence in depth, which has all been proved via deep drilling. Just like the chrome seams, Bushveld's titano-magnetite seams of the Main Zone illustrates similar continuity and persistence though, have not been extracted to date. Contained within

6392-525: The mentioned lobes. As for the center area, it is dominated by granites and other related rocks. A large metamorphic contact aureole is observed within the northern limb, the Potgietersrus area. The Vredefort impact structure is predated by the BIC intrusion and has been shown to be likely unrelated to the BIC's mineralization. The Merensky Reef can be subdivided into five layers (from bottom to top): The UG2 Pyroxenite (Reef): The host rock of

6486-660: The mine sites. There has been an increased fleeting dust generation contaminating air and water, surface water runoff is leading to a decrease in water recharge for downstream users, possibly the loss of certain vulnerable flora and fauna species, soil compaction and land erosion; the contamination and quality deterioration of the surface and ground water is driven by seepage from waste rock dumps, stockpiles, gas spills, etc. The mining activities that make large use of water could potentially lead to dewatering of local aquifers. Moreover, construction activity impacts such as removal of natural land and noise from machinery and vehicles may disrupt

6580-580: The mining companies to improve them. Between 2013 and 2016, the platinum companies contributed more than ZAR 370 million into the city; funding local infrastructure, water supply and treatment centres, sporting programmes, tourism, public road expansions, sewage treatment plants, cultural activities. The primary concern is the combination of high poverty rates and social injustice. There have been much more than 30 individual mine operations mostly mining for PGEs, some chrome, tin, and others (of which most are underground, few are open cut). These are shown below as

6674-530: The native South African tribes residing in and around the area. Located in South Africa , the BIC contains some of the richest ore deposits on Earth. It contains the world's largest reserves of platinum-group metals (PGMs) and platinum group elements (PGEs) — platinum , palladium , osmium , iridium , rhodium and ruthenium — along with vast quantities of iron , tin , chromium , titanium and vanadium . These are used in, but not limited to, jewellery, automobiles and electronics. Gabbro or norite

6768-427: The nucleus, forms it acts as a convergence point (if unstable due to supersaturation) for molecules of solute touching – or adjacent to – the crystal so that it increases its own dimension in successive layers. The pattern of growth resembles the rings of an onion, as shown in the picture, where each colour indicates the same mass of solute; this mass creates increasingly thin layers due to the increasing surface area of

6862-809: The outcrops and on mine walls. The Platreef : this reef structure is divided into three sections: The BIC contains several shear zones , some are within known faults , the most important of which are the Jagersfontein Shear Zone (JSZ), the Klerksdorp Shear Zone (KSZ), the Potgietersrus Shear Zone (PSZ), the Thabazimbi -Murchison Lineament (TML), the Brits Shear Zone (BSZ), the Olifants River Shear Zone (ORSZ) and

6956-618: The purity in a technique known as recrystallization. For biological molecules in which the solvent channels continue to be present to retain the three dimensional structure intact, microbatch crystallization under oil and vapor diffusion have been the common methods. Equipment for the main industrial processes for crystallization . The crystallization process appears to violate the second principle of thermodynamics . Whereas most processes that yield more orderly results are achieved by applying heat, crystals usually form at lower temperatures – especially by supercooling . However,

7050-421: The rate of nucleation that would otherwise not be seen without the existence of these foreign particles. Homogeneous nucleation rarely occurs in practice due to the high energy necessary to begin nucleation without a solid surface to catalyze the nucleation. Primary nucleation (both homogeneous and heterogeneous) has been modeled as follows: where Secondary nucleation is the formation of nuclei attributable to

7144-651: The region by two anticlines, namely the Katloof and Phosiri. The Merensky Reef has been displaced by 2 km to the south in the vicinity of Zebediela , as a consequence of the Madika Fault. The Madika Fault is sub-parallel to the Wonderkop Fault, which is located in the Bojanala Platinum District Municipality in the vicinity of the town of Wonderkop. The critical zone of the Rustenburg Layered Suite

7238-426: The release of the heat of fusion during crystallization causes the entropy of the universe to increase, thus this principle remains unaltered. The molecules within a pure, perfect crystal , when heated by an external source, will become liquid. This occurs at a sharply defined temperature (different for each type of crystal). As it liquifies, the complicated architecture of the crystal collapses. Melting occurs because

7332-453: The resulting crystals are generally of good quality, i.e. without visible defects . However, larger biochemical particles, like proteins , are often difficult to crystallize. The ease with which molecules will crystallize strongly depends on the intensity of either atomic forces (in the case of mineral substances), intermolecular forces (organic and biochemical substances) or intramolecular forces (biochemical substances). Crystallization

7426-444: The same deposit, are associated with mafic and ultramafic intrusions and shear zones, such as the JSZ. The general mineral assemblage of the chromitite seams in the Bushveld Complex consists of olivine + chromite, chromite +/- bronzite + plagioclase, chromite + plagioclase, and chromite + clinopyroxene. The BIC's layered sequence is commonly divided into five different zones: The area has many different ore deposits, but mostly with

7520-421: The same time a concentration of the solution. A crystallization process often referred to in chemical engineering is the fractional crystallization . This is not a different process, rather a special application of one (or both) of the above. Most chemical compounds , dissolved in most solvents, show the so-called direct solubility that is, the solubility threshold increases with temperature. So, whenever

7614-501: The so-called Critical Zone; these are referred to as reefs . The three main reef deposits are the Merensky reef , UG2 Reef, and the Platreef. These reefs are mostly continuous to discontinuous chromite layers with amounts of PGE mineralization. The surface rocks are exposed as separate lobes or limbs (the main ones being eastern, western and northern limbs) spans an area of approximately 66,000 km . This large igneous province comprises

7708-439: The soil from a tailings disposal facility had higher levels of C, N, NH 4 and K in comparison to the other general sampling sites. The difference was attributed to rehabilitation regimes being implemented reducing the abundance of these microbial and bacterial nutrients . Mining operations in general consume much energy and water, producing much waste rock, trailings and greenhouse gases. A study has shown that PGM mining has

7802-439: The soil, atmosphere and vegetation. Since some of the food production activities are located near these areas, the primary concern is that the local population (several towns and cities, including Rustenburg with more than 500,000 inhabitants ) will ultimately be exposed to the contaminants either by skin contact, dietary intake or inhalation. PGEs such as platinum, palladium, and rhodium have been shown to bioaccumulate under

7896-452: The surface through long vertical cracks in Earth's crust—huge arcuate differentiated lopolithic intrusions—creating the geological intrusion known as the Bushveld Igneous Complex. These intrusions are thought to predate the nearby Vredefort impact to the south, by some 30 million years. The effects of these injections of molten rock over time, combined with the crystallisation of different minerals at different temperatures, resulted in

7990-457: The surrounding ecosystems . Depending on the beneficiation and concentration methods, there are different impacts plausible such acid runoff from leaching and metal slimes . Hexavalent chromium from mine wastes has been shown to be highly toxic. A study has shown that up to 5% of the world total production of PGEs is lost and emitted as dust entering the global biogeochemical cycle . Nearby towns have shown elevated levels of platinum within

8084-448: The surroundings compensates for the loss of entropy that results from the reordering of molecules within the system. Such liquids that crystallize on cooling are the exception rather than the rule. The nature of the crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have

8178-424: The system, they do not have any influence on the process. This can occur in two conditions. The first is homogeneous nucleation, which is nucleation that is not influenced in any way by solids. These solids include the walls of the crystallizer vessel and particles of any foreign substance. The second category, then, is heterogeneous nucleation. This occurs when solid particles of foreign substances cause an increase in

8272-590: The three main igneous suites the Lebowa Granite Suite (large A-type granitic intrusions), Rustenburg Layered Suite (c. 8 km-thick layered mafic-ultramafic cumulate sequence), and the Rashoop Granophyre Suite (granophyric rocks). These are exposed as layered sequences of sheet like intrusions that are commonly subdivided as five main zones (from bottom to surface): Marginal, Lower, Critical, Main, and Upper Zones. These can be seen in sequence within

8366-468: The titano-magnetite ore is a persistent fractional percentage of vanadium. Reserves of the titanium and vanadium in these iron ores could potentially be very large. With that being said, it is evident that the ores existing in Bushveld occupy an important place in the world of mineral resources. Although other major platinum deposits have been found in places like the Sudbury Basin or Norilsk (Russia),

8460-442: The total world production of crystals. The most common type is the forced circulation (FC) model (see evaporator ). A pumping device (a pump or an axial flow mixer ) keeps the crystal slurry in homogeneous suspension throughout the tank, including the exchange surfaces; by controlling pump flow , control of the contact time of the crystal mass with the supersaturated solution is achieved, together with reasonable velocities at

8554-590: The transformation of anatase to rutile phases of titanium dioxide . There are many examples of natural process that involve crystallization. Geological time scale process examples include: Human time scale process examples include: Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion, also known as a salt, such as sodium acetate . The second type of crystals are composed of uncharged species, for example menthol . Crystals can be formed by various methods, such as: cooling, evaporation, addition of

8648-430: The two still dominate the market gross demand by far. That being said, the global platinum demand is still expected to increase in subsequent years to 2017. The price of platinum is quite volatile in comparison to gold, but both have greatly increased over the last century. Despite platinum being far much rarer than gold, 2014 was the last year platinum was valued at a higher price than gold (2018). This coincides with

8742-405: The work force. Miners are quite often on strike asking to get the minimum salary, and mines continue to fail safety standards and face labour unrest. A research study in 2016 by eunomix showed that Rustenburg, one of the fastest-growing cities in South Africa, has an "abnormally high concentration of young men who are separated from their families due to the migrant labour system". The population

8836-527: Was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of March 2020, this has not yet been officially adopted by the IUGS . The term Jatulian is, however, used in the regional stratigraphy of the Paleoproterozoic rocks of Fennoscandia . This is when the eukaryotes are thought to have originated from the symbiosis between asgardarchaea and alphaproteobacteria , as well as

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