Baioni Crushing Plants, leader in the aggregate crushing sector has been operating for 40 years, have recently developed equipment and methods for environmental control. Several plants have already been supplied to third parties, now Baioni have full know-how of the technology and can ensure correct conception of the line based on the specifications of the soil to reclaim and can provide technological support for the management of the line as well as suitable staff training. As each plant is made to measure according to characterization of soil to be reclaimed, with the intent to give customers the best technical and economic solution, Baioni goes all the way from investigation, process design, equipment manufacturing as well as engineering, plant erection and commissioning.
Particle size separation
“Soil washing is a water-based process for scrubbing soil ex-situ to remove contaminants and in doing so it is necessary a combination of various machines like screens and crushers, washing systems, attriction scrubbers. The complexity of this equipment is something that Baioni have been manufacturing from long, so having made a step forward has been easy for us”, says Andrea Kilchenmann, Area Manager for Baioni Crushing Plants SpA. In early 2014 Baioni have delivered and commissioned a mobile unit for the remediation and rehabilitation works at an Italian refinery owned by ENI (Italian multinational oil and gas company) with the aim at recovering sand and gravel identified as reselling valuable product in the aggregate market, while the minimun part is disposed off in landfill.
On a second stage the plant in Italy is using a special washing with water, additives and reagents, to support the physical process of washing of inert materials. The soils are thus subjected to a series of processes until the final reclamation. The water used is treated (clarified) for reintroduction into the production cycle of the plant.
“The three most important soil parameters to be evaluated during prescreening and remedy screening tests are the grain size distribution, clay content, and cation exchange capacity. Soil washing performance is closely tied to these three factors. Soils with relatively large percentages of sand and gravel (coarse material >2 mm) respond better to soil washing than soils with small percentages of sand and gravel. Larger percentages of clay and silt (fine particles smaller than 0.25 mm) reduce contaminant removal efficiency. In general, soil washing is most appropriate for soils that contain at least 50 percent sand/gravel, i.e., coastal sandy soils and soils with glacial deposits. Soils rich in clay and silt tend to be poor candidates for soil washing”, concluded Kilchenmann.
Methodology, Volumes and Equipment
The remediation entails the removal of the most heavily polluted soil - oil and hydrocarbons - around and below the area of the refinery, for an overall production of 20tonnes/hour (100 m3/h slurry flow). To protect the public roads, the refinery and the buildings on the neighbouring area against potential settlement damage, the process is carried out indoors. After the excavation, material is sent to a feed station where stones, stubs and the like are rejected on a grizzly (25mm grid bars). The processed material is then conveyed to a crusher, subsequently conveyed into a ST 200 washing trommel and deslimer for washing and frictioning. The +4mm oversize material is then simply recoverd into a RC 90 achimedean screw, water with 0,4mm material are conveyed to a cyclon unit for fines recovery; material finer than 0.03-0.1mm is normally heavily contaminated and cyclones are suitable for separation of the fines. After cycloning, the output product and the 63micron sand enter the attrition scrubber where contaminants are released from the particle surfaces by friction forces. The water with the floating organic parts are taken by a screen. Waters are then sent to a treatment process using special washings with water, additives and reagents, to support the physical process of washing of inert materials. Water used is treated (clarified) for reintroduction into the production cycle of the plant. Fractions from 0.063 to 250mm slurry resulting from the trommel and cyclone may be classified as raw material and be re-used in production processes for building or construction scopes. Fraction less than 0.063 mm resulting from treatment of sludge may be classified as secondary raw material or disposed of.