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By Paul C. Schmall, Thomas Tuozzolo, Arthur B. Corwin

The Lenox Avenue Reconstruction Project involved the excavation and replacement of 750 m (2,500 ft) of deteriorated subway invert concrete, 5 to 7 m (15 to20 ft) below water table in very permeable ground. The Replacement work was done over an 8 month period, while maintaining track service through this subway section. The project was dewatered with a single 125 l/s (2,000 gpm) wellpoint system,750 m (2,500 ft) in length, which was installed from inside the active tunnel structure and configured to coexist in the subway tunnel with operating trains as well as the construction activities. A thin diaphragm jet grout wall was utilized on one end of the site to cut off the flow of water across a difficult geological interface that was situated immediately below the tunnel invert. The thin diaphragm jet grout wall permitted the large 116th Street Station area to be dewatered completely with well points from outside of the excavation.

Jan 1, 2001

By Morgan Walker

ONE of the most serious problems in the produc- tion of natural gas is the removal of water from the wells. As a gas well approaches its period of exhaustion, the removal of water by properly de-signed devices becomes increasingly important. Sev-eral methods are used for dewatering gas wells. If the .gas velocity and pressure are high enough, the water in the well will be carried out by the gas on opening the well to atmospheric pressure and allowing the gas to flow unrestricted except for the resistance of the casing. This method of dewatering a gas well is detri-mental to the producing sand, and very wasteful if used frequently. When the well has declined in production a string of tubing is often run in the well, with a packer set at the top or bottom of the well. If the top of the tubing is opened to atmospheric pressure and the gas is allowed to flow unrestricted as in the above method, the water can be discharged at the top of the well, provided the velocity of the gas is high enough. However, if the water has accumulated in the well until the water pres-sure is equal to or greater than the gas pressure, the ,water cannot be brought to the surface. In dewatering :a gas well by this method the operator sometimes finds -that if the packer is set near the top of the well and -the casing is tight, the water can be blown out when .it is impossible to blow it out with the packer set at the top of the sand. This is largely due to some gas leaking into the tubing through the collars. This method of dewatering gas wells is also wasteful. Water can be pumped out of a gas well with virtually the same equipment, as used for pumping oil, but the method involves installing a separate pump for each well, and difficulties are encountered in attempting to pump water under high gas pressure.

Jan 3, 1927

BHP Minerals Ltd operates an open cut iron ore mining operation on Koolan Island, off the coast north of Derby in the Kimberley region of Western Australia. The mine comprises a number of pits, the largest of which is situated adjacent to the coast on the southern side of the island. The lowest bench is currently at RL +2 m, and the mine has planned ultimate depth of RL -82 m. Mining has already extended below the pre-existing water table level, and below mean sea level. In 1984, an extensive program of drilling, geophysics and test pumping was instigated to evaluate the aquifer hydraulic properties and the nature of the groundwater flow regime. With the aid of computer modelling, predictions have been made of the likely dewatering and depressurization requirements, and a conceptual pumping and drainage system has been designed.

Jan 1, 1986

By K Sommerville

BHP Billiton’s Area C iron ore operation has been in production since 2003. During 2010, below water table mining in the Marra Mamba formation commenced and dewatered ore has been successfully processed through the plant.The ability to mine below water table material increases reserves. Pits can be dewatered using a combination of ex-pit and in-pit bores. Critically it is important to allow suffi cient lead time to dewater. For Area C, in-pit bores yield the most water which presents challenges in every day operations when mining around bores. Operationally there are steep learning curves in obtaining equipment, training personnel and setting up infrastructure. Core risks include lifting, refuelling and maintaining gensets. The pipework, extraction and re-establishment work can be very manual.The challenges include blasting, mining, stockpiling, processing, water balance and disposal. Maximising up time on bores whilst minimising impacts to blast practices have evolved. Blast practices now align bores to the edge of patterns. Protecting bores have evolved from stemming bores with rock and re-drilling to using gas bags which require no drills. Based on moisture and material properties, mining of dewatered material can be categorised into three groups:1. normal,2. sheeting, and3. sheeting and top loading.Ore can go straight to the plant ore to drying pads where it takes between one and three months to drain.Stock management of these piles is important to ensure efficiency of the plant. Rules have been established for blending wet material to maintain feed capacity and some modifications to plants have been made. Dewatering of pits poses a challenge for water use. Initially turkey’s nests were established to capture water and use for dust suppression. As water abstraction has increased methods of management include using exhausted pits for storage and evaporators. Managed Aquifer recharge and use in potable water are being considered. An over arching coordination of the capacity and use are required.Important elements in dewatering include:• capacity models,• capital,• long to short planning,• day to day coordination, and • water level monitoring and balances. Success in dewatering requires a cross function team working towards a common goal. *This is an abstract only. No paper was provided for this abstract.*

Jul 11, 2011

By R. Asmatulu

According to Darcy's law, the rate of filtration should increase with increasing pressure drop across a filter cake. In centrifugal filtration, the driving pressure is created by the centrifugal forces applied in the free water on the surface of a filter cake. However, the pressure drop can become negative when the free water surface disappears, which makes it difficult to achieve low cake moistures. In hyperbaric centrifugal filtration, this problem is overcome using air pressure to restore the pressure differential. In the present work, various mineral and coal fines have been subjected to hyperbaric centrifugal filtration tests. The laboratory tests show that the moistures of various mineral fines, such as copper and zinc concentrates, phosphate, talc, kaolin clay, and precipitated calcium carbonate, can be reduced substantially below that achieved by conventional centrifuges. Similar promising results have also been obtained with various coal fines in laboratory and pilot-scale test programs and in full-scale plant demonstrations.

Jan 1, 2012

By R. Asmatulu

According to Darcy?s law, the rate of filtration should increase with increasing pressure drop across a filter cake. In centrifugal filtration, the driving pressure is created by the centrifugal forces applied in the free water on the surface of a filter cake. However, the pressure drop can become negative when the free water surface disappears, which makes it difficult to achieve low cake moistures. In hyperbaric centrifugal filtration, this problem is overcome using air pressure to restore the pressure differential. In the present work, various mineral and coal fines have been subjected to hyperbaric centrifugal filtration tests. The laboratory tests show that the moistures of various mineral fines, such as copper and zinc concentrates, phosphate, talc, kaolin clay, and precipitated calcium carbonate, can be reduced substantially below that achieved by conventional centrifuges. Similar promising results have also been obtained with various coal fines in laboratory and pilot-scale test programs and in full-scale plant demonstrations.

Jan 1, 2012

According to the Darcy?s law, filtration rate should increase with increasing pressure drop (?P) across a filter cake. In centrifugal filtration, ?P is created by the free water present on the surface of a filter cake. Thus, ?P can become negative when the free water disappears from the cake surface, which makes it difficult to achieve low cake moistures. In the present work, we have developed methods of overcoming this problem by either increasing the air pressure inside or applying vacuum outside a centrifuge. Laboratory dewatering tests conducted using these provisions showed that the moistures of various minerals and coal fines can be reduced to the level that can obviate the need for thermal drying. The new concept has been successfully tested both at pilot- and full-scale, which lead to commercial deployment through Decanter Machine, Inc., under the trade name Centribaric® centrifuge. Keywords: dewatering, hyperbaric centrifuge, pressure drop, Darcy?s law, Centribaric® centrifuge

Sep 1, 2012

By H. C. Juvkam-Wold

The design of an aquifer depressurization system is discussed. The system uses a number of wells surrounding a mine shaft to reduce the aquifer pressure in the vicinity of the shaft. The effect of various parameters such as number of wells, wellbore diameter, time and well location is discussed. It is concluded that, with a properly designed depressurization system, the aquifer pressure and the water inflow rate to the shaft may be reduced to less than 15X of their potential values in the absence of wells

Jan 1, 1980

By H. C. Juvkam-Wold

The aquifer depressurization system uses a number of wells surrounding a mine shaft to reduce the aquifer pressure in the vicinity of the shaft. The effect of various parameters such as number of wells, wellbore diameter, time, and well location is discussed. It is concluded that, with a properly designed depressurization system, the aquifer pressure and the water inflow rate to the shaft may be reduced to less than 15% of their potential values in the absence of wells.

Jan 1, 1983

By T. M. Siew

"This paper begins with a brief discussion of the geology of the Newfoundland Zinc Mine area. The results of groundwater studies and pumping tests are then presented. It was decided that groundwater in the mine could best be controlled by conventional sump pumping and grouting. The system is fully described, as well as plans for improvements on the method. LocationThe Newfoundland Zinc Mine is located in the Great Northern Peninsula of Newfoundland, six miles northeast of Daniel's Harbour. The mine is situated at an elevation of approximately 350 feet above sea level, 5 miles farther inland , west of the long range of mountains which rise abruptly with elevations of over 2,000 feet above sea level.GeologyThe ore deposits occur in lower Ordovician carbonate rocks that form part of the stable St. Lawrence platform, which is mainly composed of (1) the lower Cambrian Labrador group, (2) the upper Cambrian to lower Ordovician St. George group, (3) the disconformity overlying Middle Ordovician limestones and shales of the Table Head formation and, (4) two overlying klippen composed of Cambrian and lower Ordovician rocks.The ore deposit is a Mississippi Valley type of the Tennessee variety, having proven are reserves of 5.3 million tons averaging 9.70/0 zinc from eleven ore zones which exist in an area of 5.5 square miles.Among these ore zones, the L zone is the major underground mining area, and is by far the largest of the known deposits. It has proven are reserves of 3.4 million tons with 11.5% zinc; this underground development has been inprogress since 1974.Stratigraphically, the orebody, which occurs about 300 feet below the disconformities between the Table Head and St. George formations, is situated in the upper St. George formationof lower Ordovician age.The upper St. George formation of the L zone is divided into three main units (Fig . I) : the underlying lower limestone the middle grey dolomite pseudo breccia unit and the overlying siliceous dolomite unit. In this area of the mine, the beds of the St. George formation dip gently west to northwest to 10 to 15 degrees. The orebody, which is generally strata controlled with a southwesterly plunge and which has the form of thin, narrow, but elongate, en-echelon ore bed s, is contained in grey dolomite pseudo breccia. Its dimensions vary from 50 to 900 feet in width and 8 to 120 feet in thickness, and the over-alllength exceed s 6,000 feet.The surficial deposit of the area is a till comprising a heterogeneous mixture of sand, gravel, cobbles and boulders, with an average depth of 20 feet."

Jan 1, 1980

By OÆBrien D. R

Up until June 1988, Mount Thorley Coal Handling and Preparation Plant disposed of tailings by two methods. Approximately half of the plant tailings was mechanically dewatered by solid bowl centrifuges mixed with plant reject and was subsequently disposed in mine overburden spoils; the remainder was pumped to tailings ponds. Both future mine planning and environmental constraints could not allow for the long term construction of more tailings ponds so, following evaluation of available dewatering technology, belt press filters were selected for the treatment of tailings in excess of the capacity of the existing solid bowl centrifuges. Commission of the four 2.5 metre wide belt press filters soon showed that marked differences in performance were experienced when treating different coal seams. Further analysis showed that the coal tailings from different seams were quite different in terms of clay mineralogy, and these differences could be correlated with varying degrees of filter performance. Poor filter performance was experienced with coal tailings rich in sodium montmorillinite clays. A number of variables were investigated including in-line mechanical mixing of flocculant and feed slurry, cation exchange reagents such as gypsum, and upstream addition of cationic flocculant. In order to achieve satisfactory performance on the worst tailings, a combination of all of the above was required. In this paper, the reasons for selection of belt press filters and the program of investigations and testwork required to arrive at satisfactory belt press filter performance for the treatment of troublesome bentonitic rich tailings are discussed.

Jan 1, 1989

By Philip E. LaMoreaux

The development of large quantities of ground water for any major use in an area is always of environmental concern to representatives of regulatory groups, citizens, agricultural and industrial users. From these concerns, state and federal congressional representatives receive a variety of impulses from their constituents and in turn begin a series of questions upon which to-base appropriate legislative actions. The kaolin industry in Georgia is substantial to the economy and the welfare of an important segment of east-central Georgia. It uses large quantities of water for processing. This constitutes an important source of income and tax revenue. Pumping test procedures to provide an accurate and efficient dewatering scheme have been developed and carried out at a number of mines in the kaolin district of Georgia. This paper highlights one such test and is directed at an assessment of the impact of this industry on ground water supplies of an area.

Jan 1, 1983

Develop a method of dewatering ultrafine mineral waste that will increase water recovery from the waste and produce a dewatered material that eliminates the need for large settling ponds. Background In the hydrometallurgical treatment of many ores and concentrates to recover mineral values, slurries of fine particles are generated. Some of these slurries settle slowly and are difficult to dewater. This inherent property causes environmental and handling problems for the minerals industry. Examples of such problem wastes are clay wastes generated during the mining and beneficiation of phosphate ores, the processing of coal to produce a low-ash material, the cleaning of bentonite, beneficiation of potash, and the recovery of mica from clay-containing ores. At the present time these waste slurries are treated by techniques such as impoundment, thickening, and thickening followed by filtration. But factors such as new environmental regulations, the loss of mineral values in the waste slurries, the need to recycle water in the processing facility, and the lack of land suitable for impounding the waste have shown that new technology will be needed in the future to handle waste slurries.

Jan 1, 1986

By F. Peer

In most coal preparation processes, water is a necessary medium, but the presence of water in coal after it has been cleaned has a negative impact on transportation costs, handling and specific energy values. The utilization of super absorbent polymers (SAP) in the nappy application is well known. The concept of utilizing these polymers was investigated for the purposes of dewatering coal and other fines, generated by preparation processes such as flotation. SAPs are granular highly cross-linked synthetic copolymers with excellent water-absorbing properties. The dewatering process is characterized by three main stages: (a) contact of super absorbent polymer with high-moisture fine coal; (b) separation of dewatered fine coal from super absorbent polymer; and (c) regeneration of used super absorbent polymer, by exploiting its response to changes in conditions such as pH or temperature. Preliminary tests showed the separation step to be very difficult. The novel idea of encasing a given amount of polymer in a water permeable cloth solved this problem (of separating the swollen polymer from the dewatered coal). Preliminary tests investigating the effectiveness of the sachets of polymer showed a drastic decrease in the moisture contents of slurries. Furthermore, it was shown that it was possible to regenerate the polymer (still within the sachets) through thermal drying. A full-scale experimental programme was then followed to accurately determine the feasibility of using sachets of SAP. The experimental variables were initial slurry moisture content and polymer dosage. It was observed that the sachets seemed to work fastest and most effectively at high moistures and also at higher dosages of SAP. Regeneration of the polymer was also investigated, using two methods: thermal regeneration and pH-induced regeneration. The experimental variables, for investigating the regeneration process, were method of regeneration and grade of water used. Thermal regeneration at 70°C seemed to work successfully. Although the cost of using thermal energy is still a problem, the safety aspect (fire hazards) has been addressed since the polymer does not ignite when heated, unlike fine coal particles that may do so. The alternative method of regeneration, which exploits the pH-sensitivity of the polymer, was less successful, and further work needs to be conducted.

Jan 1, 2003

By R. Hogg

The factors which control the dewatering of fine coal by gravity/centrifugal drainage and by gas displacement (vacuum/hyperbaric filtration) are evaluated. A generalized model is presented and used to describe dewatering kinetics and to establish dewatering limits. Applications to the design of dewatering systems for fine coal dewatering are discussed.

Jan 1, 1995

The moisture content of clean coal contributes significantly to the product's transportation costs, handleability characteristics and/or energy value. A major contributor to the total moisture is the ever increasing proportion of fine coal in

Jan 1, 1994

By B. J. Scheiner

The Bureau of Mines, U. S. Department of the Interior, is conducting research on a dewatering technique for fine particles generated during the mineral beneficiation process that will recover a portion of the water now being lost using conventional waste disposal methods and significantly reduce the time required for land reclamation. The technique utilizes a flocculant, polyethylene oxide (PEO), that forms strong stable flocs that can be dewatered rapidly on static and/or rotary screens. In field tests, phosphate clay waste has been dewatered from a nominal 2.5 percent solids to greater than 20 percent solids. In other field tests, coal-clay waste has been dewatered from a nominal 3 percent solids to greater than 55 percent solids, in addition, small-scale continuous tests have shown that bentonitic clays can be dewatered from 12 percent solids to 40 percent solids.

Jan 1, 1983

By B. J. Scheiner, A. G. Smelley

The Bureau of Mines, US Department of the Interior, is conducting research on a dewatering technique for fine particles generated during the mineral beneficiation process that will recover a portion of the water now being lost using conventional waste disposal methods and significantly reduce the time required for land reclamation. The technique utilizes a flocculant, polyethylene oxide (PEO), that forms strong stable flocs that can be dewatered rapidly on static and/or rotary screens. Infield tests, phosphate clay waste has been dewatered from a nominal 2.5% solids to greater than 20% solids. In other field tests, coal-clay waste has been dewatered from a nominal 3% solids to greater than 55% solids. In addition, small-scale continuous tests have shown that bentonitic clays can be dewatered from 12% solids to 40% solids.

Jan 1, 1985

By George E. Valadão, Iván A. Reyes, Mizraim U. Flores, Armando C. Araujo, Rubén H. Olcay

Dewatering tailings to higher grades than paste produces a stable deposit that typically does not require retention dams and is called a “dry stack.” A proposal of different dewatering techniques applied in the fine tailings produced after final desliming phase, obtained from the treating of phosphatic ores, is the main objective of this work. The dewatering techniques evaluated were column thickener, deep cone classifier, and hyperbaric filtration. Calcite and dolomite were the main mineral contained in the phosphate tailings and these have a very fine granulometry; the tailings presented different behaviours related to the dewatering technique applied. The test column thickener and deep cone classifier with the best operational parameters found to obtain a maximum percentage of solids in mass were ~ 71% and ~ 67%, with values of yield stress ~ 200 Pa and ~ 100 Pa, respectively. In the hyperbaric filtration, a cake with ~ 10% moisture was obtained. This indicates that the transportation conditions are not the same. The overflow turbidity levels obtained from column thickener and deep cone classifier test did not exceed the value 100 NTU, whilst for the filtrate of the hyperbaric filter obtained values ~ 800 NTU. It was possible to preliminary estimate the recovery direct of water, considering each dewatering technique for final disposal of the tailings. The best dewatering techniques obtained were in the following order for the disposal in phosphate fine tailings dams; the hyperbaric filter showed an excellent dewatering capacity with productions rates around 160 kg h− 1 m− 2 for moisture cake of 10%, followed by the column thickener and deep cone classifier with paste ~ 71% of solids (W/W) and high-density slurry ~ 67% of solids (W/W), respectively.

Dec 23, 2023

By A. H. Shapiro, W. –F. Leung

A decanter centrifuge of novel design was developed for the dewatering of fine-solids slurries having micrometer-range particles that form pastelike, flowable, hard-to-dewater cakes. The design combines a compound beach with a cake flow control structure that allows expressed liquid, from the cake in the dry beach region to be returned to the liquid pool while maintaining a high-solids throughput. To provide optimal performance with various operating parameters (i.e., feed rate, centrifugal gravity, pool, differential speed, concentration of feed solids and slurry type), the cake flow control is adjustable. The second part of the beach is preferably at a zero angle. Tests showed that the new design allows increases in solids dryness and solids throughput. Key words: Dewatering, Centrifuge, Slurry, Fine particles, Beach decanter, Cake-flow control

Jan 1, 2003