Greater detail on individual lime applications.
Hydrated lime or quicklime is mixed with water to give an alkaline slurry which neutralises the low pH of acids. Milk of lime can also be used to avoid the need for slurrying equipment. Often insoluble calcium salt is precipitated during the reaction which can help to remove impurities from the system.
Quicklime is mixed with cement, sand, water and aluminium powder to give a slurry which rises and sets to form honeycomb structured blocks which have excellent thermal and sound insulation properties. The heat generated when quicklime reacts with water and the alkaline conditions combined with aluminium powder generates hydrogen bubbles which cause the blocks to rise.
The heat generated subsequently causes the slurry to set. The blocks are then heated in an autoclave, which promotes reactions between calcium and silicates in the sand or PFA and gives extra strength. Dolomite lime and/or modified quicklime can be added to reduce excessive shrinkage or cracking.
Calcium Carbonate, quicklime and hydrated lime can all be used to adjust the pH of soils to give optimum growing conditions and hence improve crop yields. The use of quicklime, hydrated lime and/or blends of these with calcium carbonate and magnesium Limestone will help to speed pH adjustment which can help to treat conditions.
Quicklime can be used as a component of continuous casting lubricants, and slaked lime as a lubricant carrier in wire drawing.
Continuous casting can be used for materials based on different types of metals, such as aluminium. The molten strand passes through a cooled mould, which produces a shell of solidified metal. The skin of the metal is in contact with the mould, but high temperature lubricants prevent the solidified metal from sticking, allowing the molten core to escape. Aluminium based metals can then be used for a range of different purposes from the construction of aeroplanes to tin cans.
Quicklime is frequently used in animal feed s a source of calcium. Lime from sugar refining plants can be used as one of many ingredients needed to produce vital chicken feed supplements. A mix is created which is subsequently dried and hardened to form pellets. The supplements are given to the chickens to improve and increase the strength of their egg shells. In general, the supplement is simple, efficient and inexpensive to make and use.
In addition, hydrated lime can also be added to chicken litter, used in intensive poultry farms, to extend the life of the litter and provide a degree of protection against parasites and disease.
Hydrated lime can be used as an additive to hot mix asphalt, increasing the resistance of the asphalt to water stripping. Lime also acts as a mineral filler and as an antioxidant.
A wide number of organic and inorganic sludges can be treated using quicklime to increase solids content. Biological sludge can be sanitised by the raise in both temperature and pH, obtained by the addition of lime. Biosolids treatment up to 'Advanced Treated' is achievable with this method.
Calcium Silicate Bricks are made by mixing quicklime or hydrated lime with silica sand. The bricks are pressed into shape and then heated in an autoclave, which promotes reactions between calcium and silicates in the sand and gives extra strength.
One of the main applications of lime and its derivatives is as a raw material in the manufacture of commonly used chemicals. The two main areas of usage of lime is the production of inorganic chemicals or oil additives.
Inorganics: Lime or its derivatives are essential building blocks in the manufacture of many inorganic salts such as Calcium Phosphate, a toothpaste additive, Calcium Citrate a food and drink additive and Calcium Nitrite an additive for sludge treatment.
The construction and building industry are the major use of lime products: in 1994, for example, it used 36% of the 19 million tonnes of lime sold in the European Union, compared with 38% used in iron and steelmaking.
Initially lime was the main material used for the production of concrete, but was replaced towards the end of the 19th Century by a superior binder known as Portland Cement. Cement had many advantages over lime-based products, being produced from a wide range of raw materials, giving much greater strength, and being more consistent than natural hydraulic limes,
However, lime still plays an important part in the following areas:
Contaminated land can be treated using lime and/or lime binder mixes to adjust pH and immobilise sulphates, phosphates and heavy metals.
Flue gases and acid effluents containing oxides of sulphur can be treated by introducing limestone, chalk, quicklime or hydrated lime as a powder or slurry, promoting a reaction to form insoluble calcium sulphate or gypsum which can then be collected. If carried out under the correct conditions this process can produce a saleable gypsum co-product.
Lime is widely used in the production of water for human consumption, in fact in terms of quantity, it even competes with chlorine as the major chemical used in water treatment.
Water treatment is comprised of several basic processes, depending on the impurities that need to be reduced. They are as follows:
Overall a wide range of chemicals are used in water treatment. Lime is used both as an alkali and as a source of calcium ions.
Lime products are widely used to treat waste and effluent water in order to:
The greater use of lime than of competitive alkalis reflects its higher cost-effectiveness, its efficiency in removing most heavy metals and the better physical and chemical sludge characteristics that are generally obtained.
The continuing demand for power has resulted in an increase in the burning of fossil fuels. Many such fuels contain sulphur and the resultant emissions into the atmosphere are the principal cause of acid rain. Other sources of acid rain can be incinerators whether they burn municipal or industrial waste, clinical waste, animal carcasses or natural fuels. Almost all incinerators around the world have utilised lime as a means of removing harmful gases for many years and proved lime to be cost effective, efficient and sustainable.
Lime is sprayed into the flue gas stream in the form of a dry powder or as a suspension in water. It then reacts with the pollutants to form an insoluble salt which is easy to dispose of. In the case of desulphurisation it is possible to produce quality gypsum (calcium sulphate) which can be used as a raw material in plaster or plasterboard.
The pH of acidic ponds and lakes can be controlled and raised using hydrated lime. In general terms this creates a more hospitable environment for aquatic organisms, in particular fish. Lime is therefore used by fish farmers to maintain a suitable habitat for breeding fish.
Lime, being the most cost effective alkali, is widely used in the removal of acidic gases emitted by power stations.
Lime based techniques for the abatement of acidic gases can be divided into 5 groups:
As apples and other fruit ripen, they emit carbon dioxide. When in storage, the carbon dioxide lowers the level of oxygen in the atmosphere and accelerates the rate of deterioration of the fruit. By circulating air around the fruit and over hydrated lime, the level of carbon dioxide is reduced and the fruit remains fresh and useable for longer.
Residues from processing citrus fruits are mixed with lime, dried, and sold as cattle feed. Lime can also be used to neutralise waste citric acid and to raise the pH of fruit juices to stabilise the flavour and colour.
Although limestone is generally more cost effective in the production of glass, high calcium lime in a finely ground form can also be used under specific circumstances. Burnt lime often provides greater transparency to the glass than limestone on account of:
Both of the benefits, also reduce the requirement for costly decolouriser additives. In glass processes using medium to fine grained materials, the replacement of limestone by burned lime has been reported to increase solution rates and reduce heat requirements, therefore increasing the production capacity of a furnace.
In many countries, lime is used more for iron and steel making than for construction and building. Most of the lime used is for fluxing impurities in the basic oxygen steelmaking (BOS) process. Lime is also used in similar quantities in the following:
In fact, the BOS process replaced the Bessemer and open hearth steelmaking processes during the 1960’s and caused some major changes in both the steel and lime industries. The process is now used for 70% of the worlds steel production, with the remainder being in electric arc furnaces (EAF).
Hydrated lime helps to de-hair and "plump" hides before the tanning process is completed. Our soluble bag technology helps to reduce the effort associated with dosing lime into the washing drums.
Lime concrete or "limecrete" is made by mixing controlled amounts of sand, aggregate, binder and water. Portland Cement is normally used as the binder, although nowadays hydraulic lime or hydrated lime plus a pozzolan can also be used.
Limewash is a traditional form of paint, used for the internal decoration of buildings with solid walls but without damp-proof courses. The moisture content of such walls is frequently high and varies with the seasons, meaning any wall decoration has to be porous.
Limewash is also widely used in agricultural buildings due to its mild germicidal qualities coupled with its ease of application and relatively low cost. In addition, it has also been recommended by the Building Research Establishment (BRE) for use on bituminous surfaces, such as flat roofs to reduce radiant heat absorption from sunlight.
Similar to the production of concrete and plasters, lime was the initial ingredient that was slowly replaced by Portland Cement that proved to be more beneficial due to its consistency and rapid development of strength. These cement-sand mortars however, proved to be almost too strong for most purposes, and the introduction of cement-lime mixes were proposed in the late 1800’s. This mix provided an even more efficient mix possessing both good ‘soft’ properties as well as controlled strength.
The benefits of using lime and lime-cement mortars can be divided into two categories; ‘soft’ and ‘hard’ characteristics. They are as follows:
Certain oil additives (including those used for motor vehicles) are produced by reacting hydrated limes with alkyl phenates or organic sulfonates. The resulting calcium soaps act as wear inhibitors, helping to reduce sludge build up and neutralise acidity from products of combustion.
By using the lime cycle, we can increase the purity and consequently the brightness of a calcium carbonate by calcining, hydrating and then re-carbonating back to calcium carbonate. This process is used to make fillers and coating products which are used within the paper industry.
The caustic properties of hydrated lime are used in the sulphate process during the manufacture of paper and pulp. About 250kg of quicklime per tonne of pulp are required for causticisation.
Internal plastering is used to cover up differences in level and to provide a surface which is suitable for the final decorative finish. Until the late 1800’s, internal plasters were predominantly lime based until the advantages of gypsum and cement became apparent. These binders gave faster setting and higher crushing strengths than the traditional lime plasters.
It was subsequently found however, that the use of lime gauged with cement or gypsum, to obtain the required setting time and strength, improved both the handling characteristics and the durability of plaster. Other benefits are described as follows:
In general the benefits raised from the addition of lime in the plaster, far outweigh the small increase in raw material costs.
Quicklime reacts with any free water present to form hydrated lime. This removes water from the system and can be useful when dealing with products that are heated during the manufacturing process, such as plastic. When making plastic, if any potential water is not removed then steam bubbles may occur in the finished product, which can affect its strength and appearance. Quicklime is therefore often used in PVC and rubber manufacturing processes.
External rendering mortars are used to enhance the appearance of buildings and to make the structure waterproof. Lime renders help by acting like a sponge, absorbing rainfall then allowing it to evaporate rather than soak into the wall.
As with many lime applications, the use of lime was almost made redundant by the introduction of cement in the late 1800’s. However, it was discovered that excessively high cement contents caused problems and that the use of cement-lime mortars gave significant improvements in both the ‘soft’ and ‘hard’ characteristics.
Overall renders and plasters can be applied to a variety of backgrounds including earth (which should nearly always be rendered), stone and brick. Lime based renders now offer the best performance possible, benefits include; vapour exchange, water resistance, elasticity, compatibility with all types of background and even eco friendliness.
Buildings pre 1900 would not have been built with cement (with few exceptions in the late 19th century) but with a lime mortar. Therefore in order to conserve these buildings it is essential to use similar materials when doing so. To introduce cement or cementitious mortar would cause decaying due to the difference in chemical composition of cement and inevitably result in irreversible damage. Lime mortars, lime plasters and renders and lime putty are therefore all used for the restoration of the UK and the majority of Europe’s built heritage.
Sewage generally consists of both domestic and trade effluent. It contains suspended solids, dissolved colloidal organic matter, nutrients (phosphate and ammonia) and even heavy metals (particularly from trade effluents).
Lime products have been used extensively in the treatment of sewage for over one hundred years. Its roles have included the following:
Sewage treatment currently uses a combination of mechanical, biological and chemical processes to produce a discharge of the required standard at the lowest possible price. In most countries, the requirements for the discharged water is becoming more and more stringent, causing rapid changes in the industry which may well present huge opportunities for increased lime scales.
A wide number of organic and inorganic sludges can be treated using quicklime or dolomitic lime to increase solids content. Biological sludge can be sanitised by the rise in temperature and pH obtained by adding these materials. Biosolids treatment up Advanced Treated is achievable with this method.
Lime treatment for soils, often involves the use of quicklime, or slaked lime, either as powdered hydrated lime, or as milk of lime. The effect of adding lime to soils can be divided into three distinct stages; drying, modification, and stabilisation.
After the drying and modification stages, water is added to obtain required moisture content for consolidation. The soil is then compacted to reduce the level of air voids to no more than 5%, ensuring that the stabilisation reaction proceeds in the compacted state and results in a homogenous, impermeable and stable layer. The stabilised layer has a low and acceptable shrink-swell potential, and improved compressive, tensile and flexural strengths. It also reduces the susceptibility of the stabilised layer to frost damage.
Lime is used for the treatment (neutralisation) of many waste streams.
Hydraed lime or quicklime is mixed with water to give an alkaline slurry which neutralises the low pH of acids.
Milk of lime can also be used to avoid the need for slurrying equipment. Often insoluble calcium salt is precipitated during the reaction which can help to remove impurities from the system.
Hydrated lime suspensions or milk of lime is used to neutralise and coat wire after it is acid cleaned. This acts as a slip agent to reduce friction during the drawing process and helps protect the wire during storage.