SEPARATION OF SOLIDS FROM LIQUIDS AND TAILING DEPOSITS PRESENTED BY : ANKITA SARAF-2013UGMM058 ; PRIYANKA SINHA-2013UGMM067 ; ANSHIKA RAJ-2013UGMM th Semester, Metallurgy & Materials Engineering National Institute of Technology, Jamshedpur

 Mechanical separation of solids from liquids is accomplished by one of the two general procedures i.e. thickening & filtration.  Ultimate moisture removal is obtained by drying.  Drying partakes of industrial chemistry rather than that of mineral dressing since a change of phase is involved for one of the products.

 In thickening, a suspension of solids in a liquid is allowed to settle until a clear liquid layer tops a mud layer, the clear liquid is withdrawn from the top of the thicker as likewise the mud from bottom, the operation is continuous. For its success thickening depends upon execution of the following steps: 1 Flocculation of the minute solid particles so as to form aggregates or flocs of many particles. 2 Sedimentation of the liquid laden flocs, leaving clear supernatant liquid. 3 Compaction of the sedimented flocs. 4 Elimination of the clear fluid & of the thickened mud.

 The liquid sludge has to be dewatered and has to conform to a dry and porous form.  Aerobic stabilisation can be performed simultaneously in an activated sludge plant whereby primary and secondary sludges are continuously aerated for long periods of time.  A further reduction of the sludge weight is possible with the help of sludge drying, by evaporating the remaining bound water in the sludge.  The typical thickener is Dorr thickner.

 Filtration is the most widely used method in the treatment of sludge produced by wastewater treatment.  It can consist just in drainage though sand beds or it can be mechanical under vacuum middle or high pressure conditions which require more sophisticated equipment.  Filter presses operate applying very high pressures to the cake (from 5 to 15 bars and sometimes even more).

 PLATE FILTER PRESSES :  This pressing technique is the most widespread despite its intermittent operation and its high investment cost.

 FILTRATION CYCLE : includes closing of the press, filling, filtration, filter opening, washing.  FILTRATION CAPACITY : The production capacity of a filter press is somewhere between 1.5 and 10 kg of solid per m2 of filtering surface. Filteration time depends upon : cake thickness, sludge concentration, specific resistance, compressibility coefficient.

 Tailings (also known as slimes, tailings pile, tails, leach residue, or slickens) are the materials left over after the process of separating the valuable fraction from the worthless fraction (gangue) of an ore.gangueore  The extraction of minerals from ore can be done two ways: placer mining, which uses water and gravity to extract the valuable minerals, or hard rock mining, which uses pulverization of rock, then chemicals.placer mininghard rock mining  In the latter, the extraction of minerals from ore requires that the ore be ground into fine particles, so tailings are typically small and range from the size of a grain of sand to a few microns.  Mine tailings are usually produced from the mill in slurry form (a mixture of fine mineral particles and water).mill slurry

 TAILINGS COMPOSITION :  Common minerals and elements found in tailings include:Arsenic - Found in association with gold ores, Barite, Calcite, Fluorite, Radioactive materials - Naturally present in many ores, Mercury, Sulfur - Forms many sulfide compounds / pyrites, Cadmium, Hydrocarbons - Introduced by mining and processing equipment (oils & greases)ArsenicBariteCalciteFluorite RadioactiveMercury SulfurCadmium Hydrocarbons  Common additives found in tailings: Cyanide - as both sodium cyanide (NaCN) and hydrogen cyanide (HCN). Leaching agent in extremely dilute quantities which readily volatize upon exposure to sunlight.Cyanidehydrogen cyanide  SEX - Sodium Ethyl Xanthate. Flotation agent.Xanthate  PAX - Potassium Amyl Xanthate. Flotation agent.  MIBC - Methyl Isobutyl Carbinol. Frothing agent.  Sulfamic acid - Cleaning / descaling agent. Sulfamic acid  Sulfuric acid - Used in large quantities in the PAL process (Pressure Acid Leaching). Sulfuric acidPAL  Activated Carbon - Used in CIP (Carbon In Pulp) and CIL (Carbon In Leach) processes. Activated CarbonCarbon In Pulp  Calcium - Different compounds, introduced as lime to aid in pH control. Calciumlime

 STORAGE METHODS :

 DRY STACKING : Tailings do not have to be stored in ponds or sent as slurries into oceans, rivers or streams. There is a growing use of the practice of dewatering tailings using vacuum or pressure filters so the tailings can then be stacked.  RIVERINE TAILINGS : Usually called RTD – Riverine Tailings Disposal. In most environments, not a particularly environmentally sound practice, it has seen significant utilisation in the past, leading to such spectacular environmental damage as done by the Mount Lyell Mining and Railway Company in Tasmania to the King RiverMount Lyell Mining and Railway CompanyTasmaniaKing River

 STORAGE IN UNDERGROUND WORKINGS : While disposal into exhausted open pits is generally a straightforward operation, disposal into underground voids is more complex. A common modern approach is to mix a certain quantity of tailings with waste aggregate and cement, creating a product that can be used to backfill underground voids and stopesstopes  POND STORAGE : Tailing ponds are areas of refused mining tailings where the water borne refuse material is pumped into a pond to allow the sedimentation (meaning separation) of solid particles from the water. The pond is generally impounded with a dam, and known as tailings impoundments or tailings dams.miningpond sedimentation

 SUBMARINE TAILINGS : Commonly referred to as STD (Submarine Tailings Disposal) or DSTD (Deep Sea Tailings Disposal). Tailings can be conveyed using a pipeline then discharged so as to eventually descend into the depths. Practically, it is not an ideal method, as the close proximity to off-shelf depths is rare. When STD is used, the depth of discharge is often what would be considered shallow, and extensive damage to the seafloor can result due to covering by the tailings product. It is also critical to control the density and temperature of the tailings product, to prevent it from travelling long distances, or even floating to the surface. The Solwara project being commenced in the Bismarck Sea by Nautilus Minerals proposes to use a modified STD method back down to depths below 1500 metres.SolwaraBismarck SeaNautilus Minerals

 PHYTOSTABILIZATION : Phytostabilization is a form of phytoremediation that uses plants for long-term stabilization and containment of tailings, by sequestering pollutants in soil near the roots. The plant's presence can reduce wind erosion, or the plant's roots can prevent water erosion, immobilize metals by adsorption or accumulation, and provide a zone around the roots where the metals can precipitate and stabilize.phytoremediation  DIFFERENT METHODS : Considerable effort and research continues to be made into discovering and refining better methods of tailings disposal. Research at the Porgera Gold Mine is focusing on developing a method of combining tailings products with coarse waste rock and waste muds to create a product that can be stored on the surface in generic-looking waste dumps or stockpiles.Porgera Gold Mine

 From Wikipedia (  Principles of Mineral Dressing By ‘A.M. Gaudin’  Encyclopedia Britannica Online.  From Science Direct. (