SLAKED LIME

Slaked lime, known as Calcium Hydroxide or Hydrated Lime, is an inorganic compound with the chemical formula Ca (OH) 2. The raw material for this product is Limestone. It is a colourless crystal or white powder and is produced when quicklime (calcium oxide) is mixed with water. It has many names including hydrated lime, caustic lime, builders’ lime, slack lime, and pickling lime.

At ambient temperature, calcium hydroxide dissolves in pure water to produce an alkaline solution with a pH of about 12.5. Calcium hydroxide solutions can cause chemical burns. Aqueous solutions of calcium hydroxide are called limewater and are medium-strength bases, which reacts with acids and can attack some metals such as aluminum while protecting other metals, such as iron and steel, from corrosion by passivation of their surface.

The significant application of calcium hydroxide is as a flocculant in water and sewage treatment. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide.

It is also used in fresh-water treatment for raising the pH of the water so that pipes will not corrode where the base water is acidic, because it is self-regulating and does not raise the pH too much.

Another large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide. This conversion is part of the causticizing step for making pulp. Calcium hydroxide is typically added to a bundle of areca nut and betel leaf to keep the alkaloid stimulants chemically available to enter the bloodstream via sublingual absorption.

Characteristics and Challenges Hydrated lime requires care during handling both to prevent it from escaping into the surrounding atmosphere, but also to avert contamination of the hydrated line from any airborne particles. Caution should be exercised to shield the hydrated lime from moisture or from contaminants containing moisture, which may trigger a chemical reaction that results in unexpected heat generation.

Caution should be exercised to shield the material from moisture or from contaminants containing moisture, as hydrated lime is exothermic. At the same time, priority should be given to efforts for the protection of operators and other handlers of hydrated lime, as depending on the grade of material, hydrated lime is usually given an MSDS health (H) ranking of between 1 and 3 (progressively indicating a higher level of hazard) for its corrosive effects on the skin and eyes. Severe overexposure to hydrated lime by inhalation can produce lung damage, choking, unconsciousness or death. Because of these conditions, an airtight connection all the way from the storage vessels through to the processing equipment is strongly recommended.

Experienced handlers of hydrated lime have observed that no two samples are exactly alike. On average, hydrated lime has a bulk density of 40 lb/ft 3 and is a soft and somewhat sluggish powder that has a tendency to pack or smear. In some cases however, the hydrated lime will do neither, but may instead contain abrasive crystals. Hydrated lime has been known to “rat hole” or bridge in silos, bulk bags and feeder hoppers, stick to the sides of containers, flood while being fed into conveyors and build up inside the convey lines. Hydrated limes with the same bulk densities often have different characteristics. These variations and other features usually necessitate versatile handling equipment to successfully move it as well as consultation with an expert before deciding on a suitable solution.

If the hydrated lime arrives at the processing facility in bulk bags, the frames used to discharge the bags should be equipped with additional accessories to eliminate any agglomerations and completely empty the hydrated lime from the bag. This includes features such as spring-loaded frames that will stretch the bags as they empty and lighten, making them rigid and removing any pockets of hydrated lime cornered in the bags. Bag activating devices are usually effective in agitating the hydrated lime, dislodging collections of hydrated lime closer to the bag spout, promoting a better flow. Some of these bag activating devices also serve as an airtight seal between the bulk bag and the receiving hopper.

The hoppers between the discharge bags and the conveying line should be designed with proper geometry and may need to incorporate devices such as vibrators or air fluidizers to remove hydrated lime from hopper walls as well mechanical agitators to promote flow.

If the hydrated lime is packaged in smaller bags, a bag-breaking station with a dust hood, filtration devices and a reverse pulse jet which pneumatically cleans the filter media, blowing the trapped dust back into the receiving hopper, is likely sufficient to support the manual unloading of the material. A hopper screen above the receiving vessel will help protect the operators if the hydrated lime is being dumped manually into a hopper that is equipped with agitating devices.

If the hydrated lime is being pneumatically conveyed into a processing system, the blower used to move the airline must be sized to meet the demands of system. The pneumatic conveying line for hydrated lime should be as short as possible. The number of bends in the line should be kept to a minimum. The velocity of the conveying line should be reduced if the hydrated lime begins to build up inside the line. If a flexible screw is being used to convey hydrated lime, a screw with a wider, flatter surface than the standard-sized screw is a safer choice. A beveled edge screw is usually an effective choice to eliminate the build-up of hydrated lime on the inner wall of the conveying tube. Due to the sticky nature of hydrated lime, a higher-rated horsepower motor may be required.