Tailings pipelines

The tailings from the various flotation stages of an industrial separation process can be combined and hydraulically transported by pipeline ([90,606], see also Section 10.2). Sometimes the tailings pipelines are dose to the separation plants, and therefore are of modest length, but it is not uncommon for such pipelines to extend for several tens of kilometres to a settling basin. 

FIGURE 1-11 Block diagram for thickening and disposal of tailings, used as the basis for the design of slurry concentrate and tailings pipelines. 

FIGURE 4-18 Tailings pipelines follow the slope of the hills and use soil friction produced hy partial burial as an anchor. 

These are general guidelines, but the consultant engineer should collaborate closely with the manufacturer. For example, certain special anti-thermal-breakdown additives are used with some rubbers to exceed the limit of 28 m/s or 5500 ft/min on tip speed. In certain situations, a metal impeller may be installed with rubber liners, particularly when there are concerns about slurry surges (water hammer) in tailings pipelines. 

Thickeners (Figure 12-3) are considered the starting point of tailings and concentrate slurry pipeUnes. For tailings pipelines, they feed directly into the tailings sump, but for concentrate pipeUnes they feed special storage tanks with agitators. 

The sump for the tailings pipeline (Figure 12-4) may be buUt of concrete or rubber-lined steel. A number of pipes are instaUed in the feed side such as ... 

TABLE 12-4 Checklist for Capital Costs Estimate for a Tailings Pipeline... 

Transportation. For short distances from the mine, transportation (qv) is by tmck or conveyor belt. Rail transportation is generally used for greater distances. Slurry pipelines (qv) ate being considered as an alternative. Rail transport over hundreds of kilometers results in loss of surface material in uncovered cats and a tendency to overheat in bottom-dumping tail cats owing to air infiltration around the cracks (31). Proper sealing and covets permit shipping over hundreds of kilometers. 

Dry soHds, such as as-rnined ore, emshed ore, and dried concentrates, are transported using tmeks, rail cars, ore passes, conveyor belts (see Conveying), or slurry pipelines (qv) as dictated by the logistics, distances involved, and capacity. Within the mill, conveyor belts are more common, but for fine particles, tailings, and coal, slurry transportation is more typical. 

Following pipeline transport and deposition into a tailings pond, the coarse sand fraction will begin to settle out and can be dredged and used to form beaches and dykes around the tailings ponds, for containment [606], This is not as straightforward as it may seem and the material properties of these barriers must be carefully controlled since poor construction, or subsequent events like erosion or liquefaction of the solids can cause severe failures, with catastrophic results [606],... 

The first tailings pond was located near the ore dressing plant. After 6 years of operation its capacity was exhausted and the only available area was 10 km away. This required the construction of a pipeline and pumping stations. Meanwhile, several sections of the new tailings pond have been completed and recultivated. 

The treated gas had to meet typical pipeline gas specifications, that is, less than 4 ppm vol. H2S and less than 2.0 vol.% CO2. The add gas liberated is sent to conventional two-stage Claus units followed by a Sulfreen tail gas treating unit. Figure 10.4 illustrates the original amine sweetening units process flow-scheme. There are two identical trains, each equipped with two high-pressure absorbers and two regenerators. 

The method for solids transported in slurry form is called hydraulic transportation. Today there are long distance rubber lined pipelines carrying a variety of minerals such as coal, limestone, rock phosphate, copper concentrate, nickel refinery tailings, iron ore concentrates and tailings in various parts of the world. The most important slurry pipelines in operation around the world are given in Table 4.2. 

Route of pipelines must avoid electrical cables, heavy traffic, hot areas Detectors and warning devices for CO leak Flameproof fittings, photocell-actuated gas control valves Induced Draught (ID) fans and tail gas scrabbers (if the gases contain H2S or other sulphurous compounds)... 

The system of spent fuel discharge from fuel assemblies includes the inlet pipeline for ball transport and a stop valve in the tail part of a fuel assembly, the electromagnetic drive of the stop valve, and an internal repository of spent micro fuel elements. 

FIGURE 4-19 Pipeline carrying taconite tailings with an important portion of coarse particles required pipe bridges to avoid blockage after shutdown or power failure. 

Gravity sedimentation is classified as thickening or increasing the concentration of the feed stream, or clarification or the removal of solids from relatively dilute streams. The former is used to prepare the feed for tailings and concentrate pipeline flow, or for the removal of tailings on trucks. The latter is more frequently used in sewage and waste treatment plants, where the volume of solids is considerably smaller than in tailings and concentrate flows. 

TABLE 9-3 Examples of Installation of Piston Diaphragm Pumps on Slurry Pipeline and Tailings Applications... 

Submarine pipelines are widely used in the oU and gas industry. For slurries, difficult accesses with possible sedimentation of coarse particles tend to be discouraging. Submarine slurry pipelines are typically limited to nonsetfllng slurries for tailings disposal, or to relatively short distances. 

Codelco in Chile is one of the largest producers of copper in the world. To dispose tailings to the Ovejeiia Tailings Dam, slurry had to be piped from an elevation of 4000 m above sea level down to 700 m via a 57 km (36 mUe) long pipeline. At the dam, the coarse and fine are separated using a cyclone station. Three Wirth positive displacement pumps are then used to pump the coarse material around a 4 km loop at a flow rate of 140 m /hr (616 US gpm) and at a pressure of 4.0 MPa (580 psi) (Figure 11-11). 

FEASIBILITY STUDY FOR A SLURRY PIPELINE AND TAILINGS DISPOSAL SYSTEM... 

A consultant engineer has to convince his clients of the merits of a slurry pipeline over alternative methods of transportation, whether it is for tailings disposal or concentrate shipping. One very important step in the design of a slurry pipeline is to appreciate the economics involved in the process. There is no question that this is the effort of a team of... 

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