Separation, solid-liquid clarifying

The separation of solids from liquids forms an important part of almost all front-end and back-end operations in hydrometallurgy. This is due to several reasons, including removal of the gangue or unleached fraction from the leached liquor the need for clarified liquors for ion exchange, solvent extraction, precipitation or other appropriate processing and the post-precipitation or post-crystallization recovery of valuable solids. Solid-liquid separation is influenced by many factors such as the concentration of the suspended solids the particle size distribution the composition the strength and clarity of the leach liquor and the methods of precipitation used. Some important points of the common methods of solid-liquid separation have been dealt with in Chapter 2. 

Qu and Qc, and solids concentrations of Cu and Ca, respectively. The most desirable division of solids in a device for solid/liquid separation, such as a thickener (described in Chapter 5), is where all of the solids report to the underflow so that the overflow is clarified liquid and consequently Ca is zero. If the efficiency of separation (E) is defined as the mass ratio of solids (of all sizes) in the underflow to that in the feed, then a clarified overflow corresponds to an efficiency of 100 per cent. 

Many industrial processes begin with a leaching step, yielding a slurry that must be clarified before solvent extraction. The solid-liquid separation is a costly step. The solvent extraction of unclarified liquids ( solvent-in-pulp ) has been proposed to eliminate solid-liquid separation. The increased revenue and reduced energy cost make this an attractive process, but many problems remain to be solved loss of metals and extractants to the solid phase, optimization of equipment design, effluent disposal, etc. 

Purpose (circle those which apply) recover solids, dewater solids, wash solids, classify solids, recover liquor, clarify liquor, separate 2 liquids,... 

The Air Quality Control Systems (AQCS) using lime/limestone wet scrubbing have three basic types of chemical process equipment (1) scrubbers, (2) reaction tanks, and (3) solid-liquid separators, in addition to several auxiliary pieces of equipment such as pumps, demisters, and reheaters. The SO2 in the flue gas is transferred into the liquid in the scrubber, the sulfur in the liquid is converted to solid calcium sulfite, and calcium sulfate in the reaction tanks and solid calcium sulfite and sulfate are separated from the liquid and disposed from the solid-liquid separators such as clarifiers, vacuum filters, and ponds. 

Solid-Liquid Separators. Most of the SO2 transferred from the fine gas into the liquid in the scrubber is converted to solid sulfur compounds in the scrubber and in the reaction tanks. The solid sulfur compounds and the fly ash collected in the scrubber have to be separated from the liquid and disposed of in a way that does not cause water pollution. Clarifier-thickeners, vacuum filters, ponds, etc., are being used as the solid-liquid separators. The liquid is returned to the system, and the solids are removed as waste. 

The solids concentration of the underflow from the clarifier-thickeners is between 20 and 40 wt % and is not concentrated enough for transportation by either trucks or railroad cars to the disposal areas. For this reason vacuum filters are usually used to concentrate the underflow to 60-80 wt % solids. Ponds are also being used to store solids and to accomplish solid-liquid separation. C-E is doing developmental work to determine the leaching characteristics of the sulfur compounds present in the sludge and also to determine the most suitable filtration system for lime/limestone wet scrubber systems. 

The PAC activated slndge system is a modified activated sludge process. PAC is added to the aeration tank where it is mixed with the biological solids. The mixed liquor solids are settled and separated from the treated effluent in a gravity clarifier. Polyelectrolyte will normally be added prior to the clarification step to enhance solids-liquid separation. If phosphorus removal is necessary, alum is often added at this point. Even with polyelectrolyte addition, tertiary filtration is normally required to reduce the level of effluent suspended solids. The clarifier nnderflow solids are continuously returned to the aeration tank. A portion of the carbon-biomass mixture is wasted periodically to maintain the desired solids inventory in the system. 

As the MBR process does not need the secondary clarifier for the solid-liquid separation, it can prevent these inherited problems that occur in the conventional processes for the wastewater reclamation (29). The resulting high-quality and completely disinfected effluent means that the MBR process can be used for many purposes, i.e., industrial and municipal wastewater treatment and reuse (30). More important, the land requirement of MBR is much less than that of conventional wastewater reclamation processes. 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

The WRS includes two clarifiers, two thickeners, two filter presses, and auxiliary equipment. The ICB effluent is transferred to the WRS clarifiers, where a polymer will be injected to provide chemical coagulant for enhancing removal of suspended solids. The clarified effluent will be transferred to the BRS. The clarifier sludge will be pumped to the WRS thickeners, where a polymer may be added to enhance thickening. Thickener overflow is recycled to the clarifiers, and underflow is pumped to the dewatering filter presses. The Alter press separates the solids from the liquid stream. The liquid is recirculated to the clarifiers, and the filter cake, containing 20-25 percent dry weight sohds, is a secondary waste. 

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