Limestone is used in almost everything from the construction industry and steelmaking to everyday life. A lot of mineral processing plants still do not know enough about it, and can not give full play to its value, greatly affecting the profit of the mine. In this article, we will take you to understand limestone from 5 aspects, and help you to improve the economic benefits of mining and processing.
Ⅰ.What is Limestone
Limestone is a kind of sedimentary rock whose main component is calcium carbonate (CaCO3). It is usually deposited from the bones and shells of marine organisms. Limestone bubbles violently when it encounters hydrochloric acid and releases carbon dioxide.
Color: It comes in a variety of colors, including white, gray, beige, and light yellow. Sometimes there are also darker colors due to impurities, such as greenish gray and black.
Physical Properties: Mohs hardness is 3-4, soft texture. It has particles of varying sizes and is either crumbly or non-crumbly.
The value of limestone is determined by the purity of calcium carbonate. Impurities such as clay or iron can affect the nature and use of your limestone. Limestone is usually categorized into three grades: high purity limestone (≥95% calcium carbonate) is used in high-end fields; common limestone (80%-95%) is used in construction and cement production; and low purity limestone (<80%) can only be used as a filler and is the least expensive.
Ⅱ.The Formation and Origin of Limestone
Limestone is widely distributed in ancient marine sedimentary regions, and the formation is very long. It has two main ways of formation:
The first is biological deposition. When marine organisms died, their skeletons piled up on the seabed. After hundreds or thousands of years of compression and calcification, limestone was formed. The second is chemical deposition. Calcium carbonate-rich water precipitates under specific conditions to form. Stalactites are typical examples.
Limestone is abundant and concentrated in shallow waters from 30°N to 30°S latitude. China is the world’s largest producer of lime, mainly in Guangxi, Guizhou and Hunan provinces, where it is mostly mined in large-scale open pits. The Midwest of the United States and the Indian state of Rajasthan are also high-quality limestone producing areas. In addition, Russia, Brazil, Australia and other countries also have sizable limestone reserves.
If you’re choosing a limestone quarry to mine, evaluating limestone purity and understanding the geology and transportation conditions first are key to reducing costs.
Ⅲ.The Difference between Limestone, Lime and Slaked lime
These three materials are closely related but chemically different. Many mines confuse these three concepts, resulting in the sale of the wrong products and loss of profit. Read the following table to help you quickly distinguish:
| Name | Chemical formula | Core properties | Processing method | Reference price (tons) |
| Limestone | CaCO3 | Bubbles upon contact with hydrochloric acid, relatively soft | Mining directly in the mine | 80-200RMB |
| Lime | CaO | Exothermic upon contact with water, highly corrosive | Limestone is calcined at high temperatures (above 900°C) to obtain | 300-600RMB |
| Slaked lime | Ca (OH) 2 | powder, strongly alkaline and hygroscopic | Add water to lime | 500-1000RMB |
Interestingly, limewater is prepared using slaked lime plus water, and then by passing carbon dioxide into the water you again get a milky white suspension containing calcium carbonate (CaCO3). It’s a limestone cycle.
In addition, all three have different uses. Limestone is mainly used for building aggregates, cement raw materials and fillers; quicklime is mainly used for steel desulfurization, sewage treatment and soil improvement; and slaked lime is used for pharmaceutical excipients and food additives. Both quicklime and slaked lime are products produced from limestone. If you can adopt the right steps and use the appropriate equipment to process the limestone, your profit will be directly doubled.
IV. Limestone and Cement Production
The production of cement is the most important use of limestone. Limestone accounts for more than 70% of the total raw materials for cement production and is the key raw material for cement production. Cement producers are the mine’s largest downstream customers – a source of profit.
Limestone is processed by crushing or grinding to become a basic raw material for a wide range of industrial and construction applications. Crushed limestone aggregate can be used directly to formulate concrete and asphalt; calcined at high temperatures it can be processed into lime for cement production. If you grind limestone into a fine powder, it can be used as an agricultural soil conditioner, and can also be applied to glass manufacturing, rubber production, paint processing and other industrial sectors.
If you’re going to sell this raw material, there are a few core requirements to keep in mind. One is to control the purity of limestone. The higher the calcium carbonate content, the better the quality of the cement made. Excessive impurity content not only fails to meet production standards but also affects the strength of the cement. The second is to control the limestone particle size. The particle size of 5-20mm can meet the requirements of cement production. Third, the comprehensive utilization of waste, reduce waste, and promote green production in the mine.
Ⅴ.Is Limestone Edible?
Many mineral processing plants and ordinary people are concerned about this issue. After strict processing and high purity limestone products can be used in the food and pharmaceutical industries. Limestone ore grade is high or low, some also contain clay, silica and other impurities, consumption may cause harm to the human body.
The purity of calcium carbonate in food grade limestone should be more than 98%, and it also cannot contain impurities such as heavy metals. It can be used as a food additive in the production of bread and cookies; in the medical industry, it can also be used to make calcium tablets to replenish the calcium element needed by the human body.
Food grade limestone has the highest added value. If your goal is to provide raw materials for related companies, then you need to strictly comply with health and safety standards to avoid violating the law to the detriment of the mine.
Ⅵ. Equipment Recommendations
Crushing equipment:
Jaw Crusher: its deep crushing chamber can efficiently handle large limestone raw materials and is suitable for primary limestone crushing. Meanwhile, the equipment structure is simple and the maintenance cost is relatively low.
Double Roller Crusher: It adopts two rollers rotating in opposite direction for extrusion crushing, and the limestone particles obtained are uniform. It also features easy adjustment and smooth operation, and is suitable for limestone fine crushing.
Grinding equipment:
Raymond mill: it adopts vertical structure and comes with a grading system, which can sort the limestone while grinding. Equipment with high degree of automation, continuous production capacity, in the field of limestone powdering is very common.
Ball mill: relying on the impact of the grinding media (steel balls) and grinding effect, you can get a higher fineness of the product. At the same time, it can also realize limestone superfine grinding.
Conclusion
Limestone seems to be an ordinary stone, but in fact it has a huge profit space. Your understanding of limestone and equipment selection determines the profit of your mine. Hope this article can provide reference for you to process limestone and help you to improve your profit.
FAQs
Q:Why must limestone be used in cement production?
A:Limestone is the main source of calcium oxide in cement clinkers. Calcium oxide produced by decomposition at high temperature is the core component in the formation of water-hard minerals such as calcium silicate, which accounts for about 80-90% of the raw material and is irreplaceable.
Q:How to choose between jaw crusher and double roller crusher in crushing limestone?
A:Jaw crusher is mainly used for processing large raw materials; Roller sand making machine is mostly used for medium and fine crushing and sand making. Usually, the two machines will form a production line, with coarse crushing by jaw crusher and then sand making by roller machine.
Q:What standards does food grade limestone need to meet?
A:High purity limestone must be used and strictly processed. The heavy metal (such as lead, arsenic) content, microbial indicators, etc. must meet the national food additive standards (such as GB 1886.214-2016) to ensure that the product is safe and harmless.
Q:How to judge the purity of limestone simply?
A:The easiest way is to drop dilute hydrochloric acid (or household vinegar) on the rock and observe the intensity of the bubbles produced. The faster and more bubbles are produced, the higher the calcium carbonate content. Using laboratory instruments can help you analyze the composition more accurately.
Q:What are the key factors affecting limestone price?
A: The market selling price of limestone is mainly affected by three core factors:
Calcium carbonate purity – the higher the purity content, the greater the value of industrial applications, and the higher the selling price.
Uniformity of particle size – Ore with uniform particle size usually brings a 10%-20% price premium.
Transportation distance – the closer the distance, the lower the logistics costs. The purchase price is relatively higher and the profit margin of the mine is greater.
