Reference product: sand [kg]
Location: BR - Brazil
This dataset describes mining of natural sand from riverbed deposits and its processing. Mining of sand from riverbed deposits represents 70% of Brazilian production of sand for construction (MME, 2009), being the other 30% extracted from open pits. Pumps dredge the slurry, which consists of sand, water, clay, silt, and gravel, from the river bed. The sand is separated from the slurry and transported by a vessel to the loading ports, where the sand is washed to clean fines and transported to the storage piles and loaded in trucks for delivery (does not the delivery itself). The sand’s coproducts (clay, silt, and gravel) return to the river during the process not being recovered for economic purposes, furthermore they don’t receive any allocation. Sand is not sorted by grain size in this dataset.
The dataset includes the sand extraction and processing, as well as equipment maintenance. Machinery is taken into account within the dataset "diesel, burned in building machine", as all machinery runs on diesel. Administration buildings and the quarry’s end of life are not taken into account. Data were collected from literature and some additional data were measured in one quarry located in the state of Rio Grande do Sul, Brazil, with current technology.
The representativeness of the dataset on a national scale is low ( >1%).
[This dataset has been generated using the system model "Allocation, cut-off by classification". A system model describes how activity datasets are linked to form product systems. The allocation cut-off system model subdivides multi-product activities by allocation, based on a physical properties, economic, mass or other properties. By-products of waste treatment processes are cut-off, as are all by-products classified as recyclable. Markets in this model include all activities in proportion to their current production volume.
Version 3 of the ecoinvent database offers three system models to choose from. For more information, please visit: https://www.ecoinvent.org/database/system-models-in-ecoinvent-3/system-models-in-ecoinvent-3.html)]
Typical technology for sand dredging in Brazil.
The technology involves two steps: extraction and processing. Sand is the only product from this process, even though gravel can be extracted, it is not recovered. Suction Hopper Dredger (autonomous vessels that perform all stages of sand mining, i.e., extraction, loading, transport, and unloading) is considered. Extraction and loading stages are executed by centrifugal pumps powered by diesel engines. The pumps dredge the sand from the riverbed, along with water, clay, silt, and gravel, are extracted, forming the slurry. This fluid is pumped through the pipeline up to the vessel top where it is poured into steel sieves. Coarse materials (gravel, leaves, and sticks) are retained by the sieves and are returned to the river. The rest of the slurry (sand, water, and mud) falls into big chambers inside the vessel. Sand decants faster from the slurry, due its density and size, and deposits at the chamber’s bottom. Most of the water overflows from the vessel to the river, carrying a great amount of the mud (silt and clay). Auxiliary suction pumps drain water surplus of the sand to lower the cargo weight.
After completing the extraction and loading stages, the same vessel transports the dredged sand until loading ports. The pulp is then pumped to the loading port by pipelines to semi-closed chambers at the loading port. Sand deposits at the bottom of the port’s chambers, water returns to the river carrying part of the fines. Some companies may sort the sand by grain size in this stage. In the end, Sand is washed to clean the fines and is transported by heavy equipment to storage piles.
Dredged sand from alluvial deposits can generate several local environmental issues. Problems related with changes in the natural sedimentation process, erosion of margins, changes in the stream bed conditions, changes in the suspended sediments of river water and even problems related with local and regional sand availability. “Continued and indiscriminate sand mining not only changes the physical characteristics of the river basin environments, but also disturbs its closely linked flora, fauna, and human life” (PADMALAL; MAYA, 2014)
None of these problems were assessed in this dataset due the lack of data, but they should be taken in consideration.
For further information, please refer to Padmalal, D. & Maya, K., 2014. Sand Mining, Dordrecht: Springer Netherlands. Available at: http://link.springer.com/10.1007/978-94-017-9144-1.
[To see the image, please follow the link https://db3.ecoinvent.org/images/eedc194c-05b2-452a-bd30-06ee280b7b0c]
Image source: Bernardo Jardim Ribeiro https://goo.gl/EcJiNy