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large capacity complete river sand mining machine

large capacity complete river sand mining machine

Sand Extraction: 1. Introduction GreenFacts

Sand and gravel are used extensively in construction. In the preparation of concrete, for each tonne of cement, the building industry needs about six to seven times more tonnesof sand and gravel . Thus, the worlds use of aggregates for concrete can be estimated at 25.9 billion to 29.6 billion tonnes a year for 2012 alone. This production represents enough concrete to build a wall 27 metres high by 27 metres wide around the equator. Aggregates also contribute to 90% of asphalt pavements and 80% of concrete roads and the demand for aggregates stems from a wide range of other sectors, including production of glass, electronics and aeronautics. Added to this are all the aggregates used in land reclamation, shoreline developments and road embankments , plus the 180 million tonnes of sand used in industry. This sand and gravel are mined world wide and account for the largest volume of solid material extracted globally and the...

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The amount being mined is increasing exponentially, mainly as a result of rapid economic growth in Asia and the resulting boom in construction. A conservative estimate of 40 billion tonnes /yr for the world consumption of aggregates is twice the yearly amount of sediment carried by all of the rivers of the world. Cement demand by China has increased exponentially by 430% in 20 years, while use in the rest of the world increased by 60%. Surprisingly, reliable data on their extraction in certain developed countries are available only for recent years. Sand was until recently extracted in land quarries and riverbeds; however, a shift to marineand coastal aggregates mining has occurred due to the decline of inland resources. River and marine aggregates are now the main sources for building and land reclamation. The sand that is found in most deserts is paradoxically unsuitable for concrete and land reclaiming, as the wind erosion process forms round grains that do not bind well. On the...

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Negative effects on the environment are unequivocal and are occurring around the world. The volume being extracted is having a major impact on rivers, deltas and coastal and marine ecosystems, sand mining results in loss of land through river or coastal erosion, lowering of the water table and decreases in the amount of sediment supply. Table 1 summarizes some of the impacts that are observed. Extraction has an impact on biodiversity, water turbidity, water table levels and landscape and on climate. There are also socio economic, cultural and even political consequences. The problem is now so serious that the existence of river ecosystems is threatened in a number of locations, damage being more severe in small river catchments. The same applies to threats to benthic ecosystems from marineextraction . In some extreme cases, the mining of marine aggregates has changed international boundaries, such as through the disappearance of sand islands in Indonesia. Sand and gravel mining also...

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The mining of marine aggregates is increasing significantly and although the consequences of substrate mining are hidden, they are tremendous. Marine sand mining has an impact on seabed flora and fauna. Dredging and extraction of aggregates from the benthic zone destroys organisms, habitats and ecosystems. It deeply affects the composition of biodiversity, usually leading to a net decline in faunal biomass and abundance or a shift in species composition. Longterm recovery can occur only where original sediment composition is being restored. Aggregate particlesthat are too fine to be used are rejected by dredging boats, releasing vast dust plumes and changing water turbidity, resulting in major changes to aquatic habitats over large areas. Box : The cases of Dubai Singapore

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Erosion occurs largely from direct sand removal from beaches, mostly through illegal sand mining. In Morocco, sand smugglers have transformed a large beach into a rocky landscape. Erosion can also occur indirectly, as a result of near shore marinedredging of aggregates, or as a result of sand mining in rivers. Damming and mining have reduced sediment delivery from rivers to many coastal areas, leading to accelerated beach erosion. Onshore sand mining in coastal dune systems can also lead to long term erosion sometimes of 0.5 to 1.5 metres a year. Global average sea level rise, which is expected to reach 0.25 to 0.5 metres by 2100 under the best case scenario is particularly acute for small islands states, where retreat options are . In the Maldives, to strengthen the capital Male, a large amount of sand is being imported to be used in building higher towers and coastal protection. The sand is taken from offshore sand islands. Par...

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The mining of aggregates in rivers can have an effect on pollution and change the level of water acidity. Removing sediment from rivers causes the river to cut its channel through the bed of the valley floor both upstream and downstream of the extraction site. This leads to coarsening of bed material and lateral channel instability. It can change the riverbed itself. Incision can also cause the alluvial aquifer to drain to a lower level, resulting in a loss of aquifer storage. It can also increase flood frequency and intensity by reducing flood regulation capacity. However, lowering the water table is most threatening to water supply, exacerbating drought occurrence and severity as tributaries of major rivers dry up when sand mining reaches certain thresholds.

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Tourism may be affected through beach erosion. Sand is often removed from beaches to build hotels, roads and other tourism related infrastructure. In some locations, continued construction is likely to lead to an unsustainablesituation and destruction of the main natural attraction for visitors, the beaches themselves. Fishing both traditional and commercial can be affected through destruction of benthic fauna and agriculture could be affected through loss of agricultural land from river erosion and the lowering of the water table. The insurance sector is affected through exacerbation of the impact of extreme events such as floods, droughts and storm surgesthrough decreased protection of beaches. The erosion of coastal areas and beaches affects houses and infrastructure as a decrease in bed load or channel shortening can cause downstream erosion including bank erosion and the undercutting or undermining of engineering structures such as bridges, side protection walls and structu...

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By reducing the consumption of sand One way is to reduce consumption of sand by optimising the use of existing buildings and infrastructure. Recycled building and quarry dust material can be a substitute for sand. Despite the very high value of minerals found in the sand, it is mostly used for concrete or is buried under highways. Concrete rubble should be recycled to avoid using aggregates, at least for low quality uses. Recycling glass bottles would also reduce sand consumption. Also, substitutes for sand are available. Quarry dust could be used to replace sand in general concrete structures. The replacement of sand by up to 40% of incinerator ash exhibits higher compressive strength than regular cement mortars. Some desert sand can be used if mixed with other material. There are also alternatives to concrete for building houses, including wood, straw and recycled material. However, the current building industry is geared toward concrete know how and equipment. Training of archite...

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Sand trading is a lucrative business, and there is evidence of illegal trading such as the case of the influential mafias in India, and in Morocco, half of the sand 10 million cubic metres a year comes from illegal coastal sand mining. The lack of proper scientific methodology for river sand mining has led to indiscriminate sand mining while weak governance and corruption have led to widespread illegal mining. The lack of adequate information is limiting regulation of extraction in many developing countries. Access to data is difficult, and data are not standardised. There is collaboration/co ordination between the marine scientific research establishments and the marine aggregates industry. Except in the European Union, regulation efforts are few, especially in developing countries. Lack of monitoring systems, regulatory policies and environmental impact assessments have led to indiscriminate mining, triggering severe damage to the environment and related ecosystem serv...

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