How to identify carbonate scale?

The identification of carbonate scale mainly relies on two methods: assessment based on physicochemical properties and chemical composition analysis. Chemical composition analysis can determine the type of scale, but it is time-consuming and costly; therefore, the type of scale is usually identified by examining its basic properties and comparing them with those of various types of scale. Physicochemical assessment can be carried out by observing the basic shape of the carbonate scale. The main methods for assessing physicochemical properties are as follows: ① Carbonate scale is the most soluble among all types of scale in dilute acids; both common inorganic and organic acids can dissolve it. When using an acid to dissolve carbonate scale, a large amount of carbon dioxide bubbles are produced, which is its main characteristic. In dilute acids with a concentration of less than 5% at room temperature, carbonate scale can be completely dissolved. When 100 grams of carbonate scale is dissolved in acid, more than 20 liters of carbon dioxide gas are released. ② Another characteristic of carbonate scale is that when burned at temperatures between 850–900°C, nearly 40% of its mass is lost, due to the decomposition of carbon dioxide and water molecules. As a result of the disappearance of carbon dioxide, the scale becomes loose and soluble in water, causing the solution to become alkaline. The reaction by which calcium carbonate is converted into calcium oxide is as follows. Additionally, by observing the small amount of residue remaining after the scale has been dissolved and paying attention to the odor emitted during burning, it is possible to determine the impurities present in the scale. If the residual substance after dissolution is white, it is silicate; if it is dark brown, it is the product of corrosion. If a burnt smell is detected, it indicates the presence of organic carbon (carbohydrates); if a foul smell is present, it suggests the presence of microbial sludge.

①Carbonate scale is the most soluble among various types of scale in dilute acids; both common inorganic and organic acids can dissolve it. When using acid to dissolve carbonate scale, a large number of carbon dioxide bubbles are produced, which is its main characteristic. In dilute acid with a concentration of less than 5% at room temperature, carbonate scale can be completely dissolved. When 100 grams of carbonate scale is dissolved in acid, more than 20 liters of carbon dioxide gas are released. Another feature of carbonate scale is that when it is burned at temperatures between 850–900°C, nearly 40% of its mass is lost, due to the decomposition of carbon dioxide and bound water. As a result of the disappearance of carbon dioxide, the scale becomes loose and can dissolve in water, causing the solution to become alkaline. The reaction by which calcium carbonate is converted into calcium oxide is as follows. Meanwhile, by observing the small amount of residue remaining after the scale has dissolved and paying attention to the odor emitted during burning, it is possible to determine the impurities present in the scale. If the residual substance after dissolution is white, it is silicate; if it is dark brown, it is the product of corrosion. If a burnt smell is detected during burning, it indicates the presence of organic carbon (carbohydrates); if a foul odor is present, it suggests the presence of microbial sludge.

Method for identifying carbonate scale: In a 5% salt acid solution, most of it dissolves, producing a large number of bubbles; after the reaction is complete, there is very little insoluble material remaining in the solution.