Mining in focus
Leon Louw
In copper mining , about 80 % of the produced quicklime is used in flotation processes .
is also dependent on lime products as binder and neutraliser of acidity . Lime products are used in the petroleum industry as thickener , sealant , and pH regulator . Thermal power stations use it for sulphur sorbent or detainer , depending on the process .
Addition of lime as binding agent is used in silicic and lightweight bricks . It is also the reacting agent in lightweight concrete , and plasticiser and displacer in mortar . Furthermore , lime products are used in asphalt paving to assist with waterproofing , stabilising , and as anti-disintegrant . In the agricultural sector , lime-related products are used in soil improvements as a pH regulator and accelerant for plant nutrients . In fertilisers , it serves both as deodoriser and nutrient . It is added to insecticide and fungicide as a diluent .
Lime products have a wide application in smelters , where it is used to act as flux and binder . It also has environmental applications in the absorption of smoke gases and chimney gases and is used during bar unmoulding , as nickel precipitation catalyst , and wire production lubricant . More applications include the cyanidation of auriferous ( gold ) and argentiferous ( silver ) minerals , while it also prevents the generation of hydrocyanic acid in the cyanide hydrolysis and is used as alkalising agent in cyanidation . During alkaline flotation , it is used as pH regulator , pyrite depressant , calcium salts precipitant , and linkage of the active silica contained in clays , among others . It is also used in leaching gravels to
neutralise the residual acidity and it stabilises the clays contained in the ore .
As part of non-metallic mining activities , lime products are used as pH regulator in salt and nitrate products and as linking agent in boric acid production . It is used as the binder in obtaining granulated ulexite ( fertiliser ) and potassium nitrate and as a linking agent and depressant of the magnesium present in the brines containing lithium .
Quicklime production
Quicklime is produced by the conversion of limestone through calcining in rotary or vertical kilns . During the lime process , for every tonne of saleable quicklime produced , about two tonnes of ‘ pure ’ limestone or six tonnes of impure limestone is consumed . The limestone consumption is dependent on the type of product , limestone purity , degree of calcing , water temperature , and the quantity of waste products . For every part of lime produced , two parts carbon dioxide ( CO₂ ) are generated . A distinction is made between ‘ brown lime ’ and ‘ white lime ’, having available lime contents of 68 % and 72 %, respectively .
Soft-burned lime is the most reactive and is difficult to produce because of the delicate operating balance that must be achieved , sufficient heat to drive off the CO₂ without overheating closing the pore structures . Depending on the kiln age and design , between 200kg ( new kilns ) and 350kg ( old kilns ) of coal is required to produce one tonne of quicklime .
Application in copper production
The limestone used for metallurgical purposes must be of superior grade , have a silica and alumina content of less than 2 %, and it should have a low sulphur and phosphorus content . For fluxing , the iron content may be high , but the material must be lumpy and finely crystallised to avoid decreptitation . In a powdered form , the milled carbonates can be mixed with ore and pressed as self-fluxing pellets .
Quicklime as a flux removes impurities such as phosphorus , silica , and sulphur . In the beneficiation of non-ferrous metals , lime is used to control pH in the flotation process , to neutralise iron sulphides , and to extract and recover metals through precipitation or leaching processes .
Quicklime and hydrated lime are widely used in the flotation or recovery of many non-ferrous ores , in particular copper ore flotation in which lime acts as depressant and maintains proper alkalinity in the flotation circuit . Lime is also used in the flotation of zinc , nickel , and lead-bearing ores . In the smelting and refining of copper , zinc , lead , and other non-ferrous ores , noxious gas fumes of SO₂ can be neutralised by passing these gases through ‘ milk of lime ’ ( dilute hydrated lime in an aqueous suspension ) in a scrubber to avert the formation of sulphuric acid in the atmosphere and corrosion of plant equipment .
Quicklime is used to neutralise the acid effluents generated by the acid plants associated with copper
[ 28 ] MINING MIRROR JUNE 2018