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When evaluating mineral deposits, it is extremely important to keep profit in mind. The total quantity of mineral in a given deposit is referred to as the mineral inventory, but only that quantity which can be mined at a profit is termed the ore reserve . As the selling price of the mineral rises or the extraction costs fall, the proportion of the mineral inventory classified as ore increases. Obviously, the opposite is also true, and a mine may cease production because (1) the mineral is exhausted or (2) the prices have dropped or costs risen so much that what was once ore is now only mineral.
mining , process of extracting useful minerals from the surface of the Earth , including the seas. A mineral , with a few exceptions, is an inorganic substance occurring in nature that has a definite chemical composition and distinctive physical properties or molecular structure. (One organic substance, coal , is often discussed as a mineral as well.) Ore is a metalliferous mineral , or an aggregate of metalliferous minerals and gangue (associated rock of no economic value), that can be mined at a profit. Mineral deposit designates a natural occurrence of a useful mineral, while ore deposit denotes a mineral deposit of sufficient extent and concentration to invite exploitation.
Archaeological discoveries indicate that mining was conducted in prehistoric times. Apparently, the first mineral used was flint, which, because of its conchoidal fracturing pattern, could be broken into sharp-edged pieces that were useful as scrapers, knives, and arrowheads. During the Neolithic Period, or New Stone Age (about &#; bce), shafts up to 100 metres (330 feet) deep were sunk in soft chalk deposits in France and Britain in order to extract the flint pebbles found there. Other minerals, such as red ochre and the copper mineral malachite, were used as pigments. The oldest known underground mine in the world was sunk more than 40,000 years ago at Bomvu Ridge in the Ngwenya mountains, Swaziland, to mine ochre used in burial ceremonies and as body colouring.
Gold was one of the first metals utilized, being mined from streambeds of sand and gravel where it occurred as a pure metal because of its chemical stability. Although chemically less stable, copper occurs in native form and was probably the second metal discovered and used. Silver was also found in a pure state and at one time was valued more highly than gold.
According to historians, the Egyptians were mining copper on the Sinai Peninsula as long ago as bce, although some bronze (copper alloyed with tin) is dated as early as bce. Iron is dated as early as bce; Egyptian records of iron ore smelting date from bce. Found in the ancient ruins of Troy, lead was produced as early as bce.
One of the earliest evidences of building with quarried stone was the construction ( bce) of the great pyramids in Egypt, the largest of which (Khufu) is 236 metres (775 feet) along the base sides and contains approximately 2.3 million blocks of two types of limestone and red granite. The limestone is believed to have been quarried from across the Nile. Blocks weighing as much as 15,000 kg (33,000 pounds) were transported long distances and elevated into place, and they show precise cutting that resulted in fine-fitting masonry.
One of the most complete early treatments of mining methods in Europe is by the German scholar Georgius Agricola in his De re metallica (). He describes detailed methods of driving shafts and tunnels. Soft ore and rock were laboriously mined with a pick and harder ore with a pick and hammer, wedges, or heat (fire setting). Fire setting involved piling a heap of logs at the rock face and burning them. The heat weakened or fractured the rock because of thermal expansion or other processes, depending on the type of rock and ore. Crude ventilation and pumping systems were utilized where necessary. Hoisting up shafts and inclines was done with a windlass; haulage was in &#;trucks&#; and wheelbarrows. Timber support systems were employed in tunnels.
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SubscribeGreat progress in mining was made when the secret of black powder reached the West, probably from China in the late Middle Ages. This was replaced as an explosive in the mid-19th century with dynamite, and since both ammonium nitrate fuel-blasting agents and slurries (mixtures of water, fuels, and oxidizers) have come into extensive use. A steel drill with a wedge point and a hammer were first used to drill holes for placement of explosives, which were then loaded into the holes and detonated to break the rock. Experience showed that proper placement of holes and firing order are important in obtaining maximum rock breakage in mines.
The invention of mechanical drills powered by compressed air (pneumatic hammers) increased markedly the capability to mine hard rock, decreasing the cost and time for excavation severalfold. It is reported that the Englishman Richard Trevithick invented a rotary steam-driven drill in . Mechanical piston drills utilizing attached bits on drill rods and moving up and down like a piston in a cylinder date from . In Germany in a drill that resembled modern air drills was invented. Piston drills were superseded by hammer drills run by compressed air, and their performance improved with better design and the availability of quality steel.
Developments in drilling were accompanied by improvements in loading methods, from handloading with shovels to various types of mechanical loaders. Haulage likewise evolved from human and animal portage to mine cars drawn by electric locomotives and conveyers and to rubber-tired vehicles of large capacity. Similar developments took place in surface mining, increasing the volume of production and lowering the cost of metallic and nonmetallic products drastically. Large stripping machines with excavating wheels used in surface coal mining are employed in other types of open-pit mines.
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Water inflow was a very important problem in underground mining until James Watt invented the steam engine in the 18th century. After that, steam-driven pumps could be used to remove water from the deep mines of the day. Early lighting systems were of the open-flame type, consisting of candles or oil-wick lamps. In the latter type, coal oil, whale oil, or kerosene was burned. Beginning in the s, flammable acetylene gas was generated by adding water to calcium carbide in the base of a lamp and then released through a jet in the centre of a bright metal reflector. A flint sparker made these so-called carbide lamps easy to light. In the s battery-powered cap lamps began entering mines, and since then various improvements have been made in light intensity, battery life, and weight.
Although a great deal of mythic lore and romance has accumulated around miners and mining, in modern mining it is machines that provide the strength and trained miners who provide the brains needed to prevail in this highly competitive industry. Technology has developed to the point where gold is now mined underground at depths of 4,000 metres (about 13,100 feet), and the deepest surface mines have been excavated to more than 700 metres (about 2,300 feet).
Why do we extract, produce, and transport scarce primary materials from mines around the world, when there are abundant secondary sources throughout our cities?
Just like any product, every building has a lifespan. The valuable materials they contain &#; wood, glass, concrete, metal, electronic or industrial components &#; often end up in a landfill, incinerated, or downcycled into products of much lower economic value.
The concept of urban mining combats losing such valuable resources. It aims to reduce the amount of virgin materials we mine in the traditional sense. Let&#;s explore how these efforts are gaining momentum in Dutch cities and uncover partnerships and services that develop circular products recovering a significant amount of materials. Let&#;s see how urban jungles ring with virtual gold mines.
Urban mining is the process of recovering and reusing a city&#;s waste materials. These materials are recovered from buildings, infrastructure, or products that have become obsolete. Once an object reaches the end of its useful life&#;whether it&#;s a vehicle, electronic device, or building no longer meeting safety standards&#;its materials become ripe for reuse. While urban mining, especially for metals from cars and electronics, isn&#;t a novel concept, embracing it more broadly and actively across urban landscapes is one crucial way to preserve our limited resources and remain within our planetary boundaries.
It is just as important to ensure industries can trust in a reliable supply of high-quality secondary materials. Without this trust, industries will not adopt these materials, impeding the transition to a circular built environment. The first step in any mining process is physically searching for resources, minerals, and precious metals. For example, special imaging seen here shows Amsterdam&#;s buildings contain a wealth of steel, copper, aluminum, and lead.
Maps showing the steel and copper concentrations in buildings of Amsterdam. The brighter the color, the higher the concentration.The most common materials in the urban environment are from construction and demolition. In the EU, demolition, including renovation, generates roughly 124 metric tonnes (Mt) of waste a year, which comes close to the weight of 12,277 Eiffel Towers (SOURCE). So, what happens when a building is demolished? We estimated that 71% of demolished materials in Europe are recycled or backfilled, most of it being downcycled.
For example, concrete might find its way into road fillings but rarely into new buildings, even though its properties make it a good candidate for reuse.
Reusing these tonnes of waste materials for new construction projects has many advantages. The materials are already available in the city, so there would be no need for disruptive changes in the supply chain. This would increase resilience in the event of supply chain disruption caused by transport delays, material scarcity, or increasing material prices. For all cities with circular targets, urban mining helps to maintain the materials at their highest value for as long as possible.
Let&#;s look at the work we conducted in Rotterdam to illustrate how urban mining helps the city become circular and generate value from what was long treated as simple waste. The large harbor city has set ambitious circularity targets for , including reducing the use of primary raw materials by 50%. The city also wants to create 3,500 to 7,000 jobs that contribute directly to the circular economy.
Meanwhile, Rotterdam discards 400,000 Mt of waste every year &#; a huge opportunity for recovery and reuse. We&#;ve identified buildings in the city that are scheduled for demolition up to the year and found that they contain 817,000 Mt of materials available for harvest within that time frame. Data indicates a downcycling rate of 85%, which means there is a lot of potential not only to recycle but also to reuse, a practice that maintains the value of an existing material or building component.
Our report on how to bring residential construction in the Netherlands within planetary boundaries (Woningbouw binnen planetaire grenzen) shows that using secondary materials can reduce primary material use by 18% and CO2 emissions by 40%, especially in terraced houses. This demonstrates the value of urban mining and circular materials in reducing environmental impacts at the building level.
Tree map of the waste materials from construction and demolition in Philadelphia,While construction waste provides by far the highest tonnage in the urban mine, everything in the city can be reused at the end of its useful life. Urban mining can be applied to electronic waste, which contains a literal treasure trove of gold and other precious metals, as well as to entire products and appliances. Anything in a city is part of the urban mine. Amsterdam claimed 69,000 unwanted bicycles in alone, and fishes more than 15,000 bikes out of the canals every year. Each and every one represents valuable metals, spare parts, ready-made frames, and other components that can be reused locally or to jump-start new production processes.
However, just as big cities are called the &#;concrete jungle&#;, the buildings we see all around us are the biggest and most valuable part of any urban mine. Not just concrete, or the steel that reinforces our modern buildings, but the wood, the glass, the copper pipes, the aluminum facades, the roof tiles, bricks, or even the iron railings on our balconies. All of these are valuable finished products that have already gone through a long supply chain.
Consider the process and life cycle of a major construction product such as concrete. It starts with sourcing the materials required for its creation. Stone and sand are extracted to be used in the mixture, combined with cement, derived from limestone, silica, clay, and other materials. To reinforce concrete, steel is integrated, its production consuming 20 gigajoules of energy per ton and resulting in 1.83 million tons of CO2 emissions, alongside significant air and water pollution from iron ore mining. This amalgamation of components leads to more complex products.
Subsequent steps, including manufacturing, transportation, and labor, demand substantial time, energy, and resources, which contribute to greenhouse gas emissions and environmental impact.
Now we see that each stage, from extraction to assembly, adds value to the end product. In a low-carbon and circular construction sector, the goal is to maximize this value retention, especially in structures earmarked for demolition. By carefully disassembling buildings and repurposing materials, high-value retention is achievable.
Our partner, New Horizon, champions circular construction with its Urban Mining Concrete. This innovative solution repurposes materials from demolished sites to produce new concrete. By reclaiming sand, gravel, and active cement through their Smart Liberator technology, this concrete substantially lowers CO2 emissions, aligning with sustainability goals. Specifically, Urban Mining Concrete achieves a 60-80% reduction in CO2 emissions compared to traditional concrete.
This approach can be found for almost all materials. Another partner of ours, Luijtgaarden for example specializes in providing sustainable roofing solutions by reusing ceramic roof tiles. Each tile is carefully sorted and inspected to meet quality standards, and comes with a warranty of up to 10 years. Luijtgaarden maintain a large inventory of used tiles, ensuring a variety of options for renovation projects. This reduces construction waste and paves the circular path for the sector.
Despite this kind of innovations, broader adoption is slow, with only 8% of materials being reused in the Netherlands. Our analysis with local stakeholders in Stadregio Parkstad identified both practical and systemic obstacles to scaling the use of circular products. For instance, while refurbished ceiling panels significantly lower CO2 emissions, they face affordability challenges. The costs associated with disassembly and refurbishment, along with a reliance on subsidized labor, hinder their widespread adoption. The interplay between environmental benefits and financial viability remains one of the key complexities in the adoption of circular solutions.
At a systemic level, circular solution providers face multiple challenges. There is a lack of understanding among building owners&#;including public authorities and housing associations&#;as well as contractors, regarding potential circular solution chains and their regional or national impacts. It&#;s essential to unlock material supply and adapt processes for reusing materials from buildings, which includes revising demolition policies and fostering collaboration. Implementing circular procurement policies also demands careful consideration in the tendering processes for both public and private sectors, ensuring interdisciplinary cooperation and securing these efforts with suitable contract forms.
Meanwhile, the impact of secondary material reuse remains latent. Despite the profound impact circular building products and materials pose, adopting urban mining is limited and supply constraints diminish the strategy&#;s overall effectiveness in CO2 reduction on a larger scale.
There are systemic barriers that can only be overcome when public organizations play a pivotal role in adopting urban mining initiatives. This begins with providing the necessary knowledge and infrastructure to foster circular initiatives and ensuring that policies support the transition to a low-carbon, circular construction sector.
Ambitious cities and regions lead the transformation by taking these key steps:
This strategic focus not only aligns with ambitious policy goals for circularity in cities but also showcases the vast opportunities within the urban mine, ultimately facilitating the transition towards circular and regional supply chains.
Cities are the engines of our global economy. Home to most of the world&#;s population, they are centers of human creativity, diversity, and interaction, but their resource use and emissions extend beyond their footprint. At Metabolic we aim to reinvent our cities as healthy, sustainable, and inclusive places that foster strong communities and allow all species to flourish, while remaining within the limits of the planet. We can make this a reality by working with cities and regions to redesign our urban future.
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