What Is Quicklime a.k.a Calcium Oxide?
Quicklime, chemically known as calcium oxide (CaO), or commonly referred to as lime, is a widely used chemical compound that originates from calcium carbonate (aka limestone) which is formed when calcium carbonate is heated in a kiln through the process of calcination. Quicklime is primarily made up of calcium, magnesium and small amounts of other chemical compounds depending on the formation of the originating limestone. Quicklime derived from limestone containing less than 5% magnesium content is referred to as high calcium quicklime, and quicklime derived from limestone with higher amounts of magnesium is referred to as dolomitic quicklime.
Quicklime can also be further processed, through an exothermic reaction in a hydrator, into a chemical compound called calcium hydroxide Ca(OH)2. This process adds approximately 25% water to the quicklime, however its final form as calcium hydroxide remains a dry powder. Calcium hydroxide is typically referred to as hydrated lime, and also referenced as slaked lime, but do not confuse this with the wet slurry derived from the slaking process. While powdered quicklime is dry, it can be processed in a different manner to produce a slurry product.
Note that the term “lime” refers to both quicklime and hydrated lime, thus when differentiation is necessary, products should be referenced as quicklime or hydrated lime, because quicklime and hydrated lime products are not exactly the same.
Quicklime Products And Applications - A Widely Used Chemical Compound
Lime is commonly used to neutralize acidic compounds, adjust pH, remove impurities, disinfect, stabilize sludge, remove gaseous pollutants from exhaust streams, and dry/stabilize soils.
Many industrial processes and systems require calcium compounds such as quicklime, hydrated lime and/or limestone for specific applications, including:
- BOF and EAF steelmaking as a fluxing agent to remove impurities in the molten steel, thus achieving proper slag chemistries and physical properties.
- Power plants for utilities that burn coal or waste to generate electricity, lime is used to reduce acid gas emissions into the environment. This is referred to as flue gas treatment (FGT) or flue gas desulfurization (FGD). The primary gases that lime removes are sulfur dioxide (SO2) and hydrochloric acid (HCl).
- Non-ferrous mining uses quicklime in the beneficiation of precious metal separation to neutralize acids used to control flotation by adjusting pH levels.
- Pulp and paper uses quicklime in the process of converting wood chips into wood pulp for economical recausticization in kraft mills.
- Environmental applications benefit from the use of lime in many ways. In drinking water treatment a lime slurry addition is used to reduce hardness, remove impurities and minimize pathogens. In wastewater treatment lime is used to neutralize acidic water, remove impurities such as heavy metals and contaminants, and dry biosolids. Lime is also used to remediate waste sludge sites and neutralize acid mine drainage.
- Chemical industries use lime in various ways as a desiccant or to adjust pH. Applications include precipitated calcium carbonate (PCC) production, manufacture of alkalis, petrochemicals, calcium carbide, citric acids and many more.
- In agriculture lime is used for disinfection of animal bedding, treatment of animal waste, and purification of sugar from beet or sugarcane operations.
- The construction sector also uses quicklime for soil stabilization and drying.
Quicklime Types & Uses
With all of the different forms of quicklime, many factors should be considered when choosing which type is best suited for your application. The following are general guidelines to consider when choosing the lime product for your needs:
- High Calcium Quicklime vs. Dolomitic Quicklime
Naturally, this will be dependent on your application needs for levels of calcium and magnesium content. In steel applications, the magnesium helps extend the life of refractory, thus reducing replacement costs. In agriculture, magnesium has benefits as a fertilizer. Some FGT sites use magnesium enhanced lime (MEL) which enhances sulfur dioxide scrubbing.
- Quicklime vs. Hydrated Lime
Hydrated lime is more reactive, requires a lesser amount, does not contain grit, but also more expensive due to the extra processing. Typically, a medium-scale user (500-3,000 dry tons per year) would see benefits with hydrated lime, but anything over that amount should consider using quicklime.
- Dry Quicklime vs. Ready-Made Liquid Lime Slurry
If a lime slurry is needed for your process, the capital equipment cost could be quite high to turn a dry product into a slurry. As a rule-of-thumb, if you use <500 dry tons per year, it would be more economical to purchase a ready-made requested lime slurry concentration and have it delivered to the site, otherwise an investment in capital should be considered.
- Sizing – Pebble vs. Finely Ground
This will depend on flowability needs and first step processing. An injection system, for example, would require a smaller size to ensure it flows efficiently through small piping. However, pulverized material costs will be higher due to the extra processing step.
Quicklime does not have a long shelf-life because it quickly reacts with moisture, and other compounds, in the ambient air. Thus, it must be protected from the elements from production all the way through use in the specified application. After quicklime is produced, it is stored in a silo, then transferred into an enclosed vessel (truck, rail or barge) for transportation, and then offloaded into a silo for onsite storage until it is pulled for processing. Most of the transloading is accomplished with pneumatics.
For storage of quicklime as a slurry, it needs to be stored in a tank capable of continuously agitating the solution to prevent settling. Once the solution is needed, it is transferred via pumps at the proper feed rate.
Chemical manufacturing often involves specialized, or proprietary processes that require a consistent and economical feed of raw materials. When evaluating what lime product is best suited for your needs, several things should be taken into consideration::
- Purity and quality of raw materials
- Environmental compliance
- Existing onsite equipment
- Storage and transportation costs
- Process throughput
- Final product specifications
Why High Calcium Quicklime from Carmeuse for Your Chemical Manufacturing Needs?
- Maximum calcium content
- Low amount of contaminants
- Most cost effective form of lime when slaking onsite
- Maintains proper alkalinity and pH in the process
- Reacts in metathesis reaction
- Effective desiccant (rubber)