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45-549: New Zealand Steel Limited is the owner of the Glenbrook Steel Mill , a steel mill located 40 kilometres south of Auckland , in Glenbrook, New Zealand . The mill was constructed in 1968 and began producing steel products in 1969. Currently, the mill produces 650,000 tonnes of steel a year, which is either used domestically or exported. Over 90% of New Zealand's steel requirements are produced at Glenbrook, while

90-506: A blast furnace where the iron compounds in the ore give up excess oxygen and become liquid iron. At intervals of a few hours, the accumulated liquid iron is tapped from the blast furnace and either cast into pig iron or directed to other vessels for further steel making operations. Historically the Bessemer process was a major advancement in the production of economical steel, but it has now been entirely replaced by other processes such as

135-709: A rolling mill . Originally the minimill was adapted to production of bar products only, such as concrete reinforcing bar , flats, angles, channels, pipe, and light rails. Since the late 1980s, successful introduction of the direct strip casting process has made minimill production of strip feasible. Often a minimill will be constructed in an area with no other steel production, to take advantage of local markets, resources, or lower-cost labour. Minimill plants may specialize, for example, in making coils of rod for wire-drawing use, or pipe, or in special sections for transportation and agriculture. Capacities of minimills vary: some plants may make as much as 3,000,000 tons per year,

180-613: A continuous production campaign of several years duration. Even during periods of low steel demand, it may not be feasible to let the blast furnace grow cold, though some adjustment of the production rate is possible. Integrated mills are large facilities that are typically only economical to build in 2,000,000-ton per year annual capacity and up. Final products made by an integrated plant are usually large structural sections, heavy plate, strip, wire rod, railway rails , and occasionally long products such as bars and pipe . A major environmental hazard associated with integrated steel mills

225-587: A loss during the 1970s, until 1981 when a more optimised, commercially viable method for extracting iron was implemented, leading to an expansion of the Glenbrook facilities. In the Think Big era of New Zealand industrialisation , the mill was upgraded. In 1987, New Zealand Steel was acquired by Equiticorp. Equiticorp was bankrupted in the New Zealand sharemarket crash of 1987 . In 1989 New Zealand Steel

270-447: A mine that contribute to this load: drilling , blasting, loading, and hauling . Waste rock is hauled to a waste dump. Waste dumps can be piled at the surface of the active pit, or in previously mined pits. Leftover waste from processing the ore is called tailings , and is generally in the form of a slurry . This is pumped to a tailings dam or settling pond, where the water is reused or evaporated. Tailings dams can be toxic due to

315-429: A number of worked-out mines. After mining ends at a location, the mine area may undergo land rehabilitation . Waste dumps are contoured to flatten them out, to further stabilize them. If the ore contains sulfides it is usually covered with a layer of clay to prevent ingress of rain and oxygen from the air, which can oxidize the sulfides to produce sulfuric acid , a phenomenon known as acid mine drainage . This

360-493: A regular basis, minimills can follow the market demand for their products easily, operating on 24-hour schedules when demand is high and cutting back production when sales are lower. Opencast mine Open-pit mining , also known as open-cast or open-cut mining and in larger contexts mega-mining , is a surface mining technique that extracts rock or minerals from the earth. Open-pit mines are used when deposits of commercially useful ore or rocks are found near

405-477: A result of room and pillar mining . Untopping removes the overburden from above this, opens up the mine from above, and then allows the previously 'trapped' minerals to be won. Untopping was a feature of Welsh slate workings in the 1930s and 2000s, where Martyn Williams-Ellis, manager at Llechwedd found that earlier Victorian workings could be kept profitable with the newly mechanised techniques for bulk excavation to extract their pillars, and more recently across

450-436: A slurry and transported to the mill by an 18 kilometre long pipeline . Approximately, 1.2 million tonnes of ironsand ore are delivered to the mill annually. The area is estimated to contain over a billion tonnes. Glenbrook's iron plant contains four multiple hearth furnaces , four rotary kilns , and two melters. The kilns directly reduce the ore to metallic iron. This process is unusual as most mills use blast furnaces for

495-457: A typical size is in the range 200,000 to 400,000 tons per year, and some old or specialty plants may make as little as 50,000 tons per year of finished product. Nucor Corporation , for example, annually produces around 9,100,000 tons of sheet steel from its four sheet mills, 6,700,000 tons of bar steel from its 10 bar mills and 2,100,000 tons of plate steel from its two plate mills. Since the electric arc furnace can be easily started and stopped on

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540-450: Is a crucial aspect of determining whether or not a geotechnical engineering design for open-pit slopes is attainable. Groundwater control systems, which include dewatering and depressurization wells, may also have a large impact on local groundwater. Because of this, an optimization-based version of the control system is required to ensure that local and regional hydro-geological impacts are within acceptable ranges. Open Pit depressurization

585-468: Is a low grade ore with many contaminants, the mill's primary plants' operations and equipment are unusual. The west coast beaches of the North Island of New Zealand between Kaipara Harbour and Whanganui contain ironsand deposits rich in the mineral titanomagnetite . From the late 19th century to the 1950s, there were many unsuccessful attempts to smelt steel from the ironsands. A prize offered by

630-509: Is determined by the size of the equipment being used, generally 20–40 metres wide. Downward ramps are created to allow mining on a new level to begin. This new level will become progressively wider to form the new pit bottom. Most walls of the pit are generally mined on an angle less than vertical. Waste rock is stripped when the pit becomes deeper, therefore this angle is a safety precaution to prevent and minimize damage and danger from rock falls. However, this depends on how weathered and eroded

675-416: Is sometimes used with scrap, to help maintain desired chemistry of the steel, though usually DRI is too expensive to use as the primary raw steelmaking material. A typical mini-mill will have an electric arc furnace for scrap melting, a ladle furnace or vacuum furnace for precision control of chemistry, a strip or billet continuous caster for converting molten steel to solid form, a reheat furnace and

720-640: Is the pollution produced in the manufacture of coke , which is an essential intermediate product in the reduction of iron ore in a blast furnace. Integrated mills may also adopt some of the processes used in mini-mills, such as arc furnaces and direct casting, to reduce production costs. A minimill is traditionally a secondary steel producer; however, Nucor (one of the world's largest steel producers) and Commercial Metals Company (CMC) use minimills exclusively. Usually it obtains most of its iron from scrap steel, recycled from used automobiles and equipment or byproducts of manufacturing. Direct reduced iron (DRI)

765-401: Is the process of removing tensions or pressure from different areas of a mine. Depressurization helps to make open-pit mines more stable and secure. By using an integrated mine slope depressurization program the likelihood that mine plans can be achieved, and at an acceptable level of risk increase drastically. Depressurization allows considerable expansions of a mine, and can extend the life of

810-559: Is then generally covered with soil , and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large-scale open-pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to

855-668: The Lusatian Lake District , the Central German Lake District or the Upper Palatinate Lake District. A particular concern in the formation of these lakes is acid mine drainage . Open-pit mines create a significant amount of waste. Almost one million tons of ore and waste rock can move from the largest mines per day, and a couple thousand tons moved from small mines per day. There are generally four main operations in

900-594: The Philippines and Indonesia . In 2024, nickel mining and processing was one of the main causes of deforestation in Indonesia . Open-pit cobalt mining has led to deforestation and habitat destruction in the Democratic Republic of Congo . Open-pit mines operating in an area with heavy groundwater features may eventually face hydrology-related problems. This includes heaving and bursting of

945-567: The Taranaki Provincial Government was never claimed, mostly due to problems encountered by people attempting to process the iron sand, such as a viscous slag of titanium carbides and nitrides that forms and blocks equipment when heat is applied to the sand. In 1954, the Department of Scientific and Industrial Research began investigating smelting from the ironsands. In 1959, The New Zealand Government established

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990-434: The basic oxygen furnace . Molten steel is cast into large blocks called blooms . During the casting process various methods are used, such as addition of aluminum , so that impurities in the steel float to the surface where they can be cut off the finished bloom. Because of the energy cost and structural stress associated with heating and cooling a blast furnace, typically these primary steel making vessels will operate on

1035-418: The mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. After open-pit mines are closed, they are sometimes converted to landfills for disposal of solid waste. Some form of water control is usually required to keep the mine pit from becoming a lake. Several former open-pit mines have been deliberately converted into artificial lakes, forming areas such as

1080-815: The NZ Steel Investigating Company under the Iron and Steel Industry Act 1959 as a vehicle for the investigations. New Zealand Steel Limited was incorporated by the New Zealand Government in 1965. In 1967, construction started on a mill at Glenbrook. Glenbrook was chosen as the site due to the area's proximity to the Waikato North Head ironsand mine and Huntly Power Station . Commercial operations began in 1968, with imported feed coil being used to produce steel for domestic and Pacific Island markets. The company pioneered

1125-408: The New Zealand Government would provide funding of up to $ 140 million for an initiative to halve the consumption of coal at the Glenbrook plant and reduce carbon emissions. The project involves installation of an electric arc furnace to replace coal as the heat source for recycling scrap metal. The ironsand ore is mined at an opencast mine at Waikato North Head . The ironsand is then mixed to form

1170-402: The areas surrounding open-pit mines. Open-pit gold mining is one of the highest potential mining threats on the environment as it affects the air and water chemistry. The exposed dust may be toxic or radioactive, making it a health concern for the workers and the surrounding communities. Open-pit nickel mining has led to environmental degradation and pollution in developing countries such as

1215-463: The converter (Klöckner Oxygen Blown Maxhütte process, or KOBM converter), whereas oxygen is only blasted at the top of the converter in most steelmaking plants. Steel mill Since the invention of the Bessemer process , steel mills have replaced ironworks , based on puddling or fining methods. New ways to produce steel appeared later: from scrap melted in an electric arc furnace and, more recently, from direct reduced iron processes. In

1260-399: The direct reduction process for reducing iron oxide (ironsand) into metallic iron. This culminated in the commissioning in 1970 of iron and steelmaking facilities to produce billets for domestic and export markets. Expansion continued with the commissioning of a pipe plant in 1972 and a prepainting line in 1982. Total output at this time averaged 300,000 tonnes a year. The steel company ran at

1305-472: The environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence , to prevent access, and it generally eventually fills up with ground water . In arid areas it may not fill due to deep groundwater levels. In Germany, the world's largest producer of lignite (virtually all of which these days is mined open-pit), the former mines are usually converted to artificial lakes . To mitigate

1350-429: The hole. The interval of the benches depends on the deposit being mined, the mineral being mined, and the size of the machinery that is being used. Generally, large mine benches are 12 to 15 metres thick. In contrast, many quarries do not use benches, as they are usually shallow. Mining can be conducted on more than one bench at a time, and access to different benches is done with a system of ramps. The width of each bench

1395-673: The late 19th and early 20th centuries the world's largest steel mill was the Barrow Hematite Steel Company steelworks located in Barrow-in-Furness , United Kingdom . Today, the world's largest steel mill is in Gwangyang , South Korea . An integrated steel mill has all the functions for primary steel production: The principal raw materials for an integrated mill are iron ore, limestone, and coal (or coke). These materials are charged in batches into

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1440-454: The mine by 10 to 15 years. One technique used in depressurization is annealing. Annealing is the slow heating and cooling of a metal, alloy or glass. This slow heating and cooling relieves the internal stress of surrounding areas. Annealing will increase a material's workability and durability, which overall increases open-pit mine safety. When groundwater pressures cause problems in open-pit mines, horizontal drains are used to aid in accelerating

1485-450: The mine floor due to excessive uplift pressure. A groundwater control system must be installed to fix problems caused by hydrology. The formation of an appropriate open-pit slope design, changes throughout the life of a mine. It is based mainly on an ever-increasing understanding of the rock mass conditions, including groundwater and associated pressures that may be acting within the slopes. The reduction of groundwater related to pore pressures

1530-446: The presence of unextracted sulfide minerals , some forms of toxic minerals in the gangue , and often cyanide which is used to treat gold ore via the cyanide leach process . If proper environmental protections are not in place, this toxicity can harm the surrounding environment. Open-pit mining involves the process of disrupting the ground, which leads to the creation of air pollutants. The main source of air pollutants comes from

1575-407: The problem of acid mine drainage mentioned above, flooding is often done with the water of nearby rivers instead of using groundwater alone. In some cases, calcium oxide or other basic chemicals have to be added to the water to neutralize the pH -value. Gold is generally extracted in open-pit mines at 1 to 5 ppm (parts per million) but in certain cases, 0.75 ppm gold is economical. This

1620-429: The reduction process. In the steelmaking plant, vanadium recovery and removal is done due to the high vanadium content of the ironsand ore. The sand also contains aluminium , manganese and titanium . Oxidation of the molten metal and contaminants is achieved by a basic oxygen steelmaking facility. The process used in the converter is the second unusual piece of equipment: oxygen is blown on both top and bottom of

1665-538: The remaining volume is produced by Pacific Steel, a steel recycling facility in Ōtāhuhu , Auckland. The mill is served by the Mission Bush Branch railway line , which was formerly a branch line to Waiuku . Coal and lime trains arrive daily. Steel products are also transported daily. The mill employs 1,150 full-time staff and 200 semi-permanent contractors. New Zealand Steel is notable due to its unique utilization of ironsand as its ore . Because ironsand

1710-404: The rocks are, and the type of rocks involved. It also depends on the amount of structural weaknesses occur within the rocks, such as a faults , shears , joints or foliations . The walls are stepped. The inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or berm. The steps in the walls help prevent rock falls continuing down the entire face of

1755-412: The slope depressurization process. Which helps to prevent large scale slope failure in the mine. Horizontal drains are used to lower pore pressure by reducing groundwater head, which enhances slope stability. A form of open-cast quarrying may be carried out as 'untopping'. This is done where a previous underground mine is becoming uneconomic or worked-out, but still leaves valuable rock in place, often as

1800-558: The surface where the overburden is relatively thin. In contrast, deeper mineral deposits can be reached using underground mining. Open-pit mining is considered one of the most dangerous sectors in the industrial world . It causes significant effects to miners' health, as well as damage to the ecological land and water. Open-pit mining causes changes to vegetation, soil, and bedrock, which ultimately contributes to changes in surface hydrology, groundwater levels, and flow paths. Additionally, open-pit produces harmful pollutants depending on

1845-416: The transportation of minerals, but there are various other factors including drilling, blasting and the loading and unloading of overburden. These type of pollutants cause significant damage to public health and safety in addition to damaging the air quality. The inhalation of these pollutants can cause issues to the lungs and ultimately increase mortality. Furthermore, the pollutants affect flora and fauna in

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1890-517: The type of mineral being mined, and the type of mining process being used. Miners typically drill a series of test holes to locate an underground ore body. From the extracted samples, they can determine the extent of the ore. This helps them determine the likely location of the veins or benches of ore and its commercial value. Open-pit mines that produce building materials and dimension stone are commonly referred to as quarries . Open-cast mines are dug on benches , which describe vertical levels of

1935-466: The wall. In some instances additional ground support is required and rock bolts , cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself. A haul road is usually situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock. Open-pit mines are typically worked until either

1980-524: Was achieved by bulk heap leaching at the Peak Hill mine in western New South Wales , near Dubbo , Australia . Nickel , generally as laterite, is extracted via open-pit down to 0.2%. Copper can be extracted at grades as low as 0.11% to 0.2%. Open-pit mining is a common method to extract minerals and samples from the Earth. Due to being cost-effective, this method is very popular and is used all over

2025-596: Was acquired by Helenus Corporation, which consisted of Fisher & Paykel , Steel & Tube, ANZ Bank and BHP . In 1992, BHP took up a controlling interest with an 81% shareholding by acquiring the shares of Fisher & Paykel and Steel & Tube. The company was initially renamed BHP New Zealand Steel Limited, then in 2002 was renamed New Zealand Steel when BHP Steel was listed on the Australian Securities Exchange as BlueScope . On 21 May 2023, Prime Minister Chris Hipkins announced that

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