Heavy liquid method is the most accurate measure for nondestructive separation of material, and the most accurate method for accurately measuring the relative density of single grain material. Usually, the heavy liquid can be divided into three categories as following:

1. Halogen hydrocarbons which have the relative density within 0.86 ~ 3.32, but they are very easy to volatilize with a small viscosity and poison; 

2. Salt aqueous solution which has the big proportion, and easily soluble, with its relative density of 1.0 ~ 4.3, however, most of them are expensive, or with the property of unstable, toxicity, easy to react; 

3. Salts and their mixture with low melting temperature, while the specific gravity can reach to 4.7, and the nitrate or halide with mercury, silver, thallium, tin, antimony is generally used. The defect of this kind of heavy liquid is that the temperature should be raised when it is used, and mostly of them will easily react with water and minerals, and the extremely toxic. 

 

The different relative density of heavy liquid can be formed from the soluble salts and solvents with different proportion in accordance with the variety relative densities of the staying separation of the substance. A new type of non-toxic heavy liquid can be obtained by using ammonium metatungstate to dissolve in water. Ammonium metatungstate (AMT) is a substance which is easily soluble in water, with the largest solubility in water among all tungsten compounds. 

 

Compared with the most existing heavy liquids, this new type of ammonium metatungstate non-toxic heavy liquid has the advantages of non-toxic, tasteless, fairly viscous, medium cost and so on, thereby to eliminate the pollution to the environment, protect the health of operators and improve the work efficiency; therefore, it can be applied to the nondestructive inspection and determination of solid materials with relative density less than 3.6 which includes crystallization of minerals, industrial products, amorphous glassy material and the solid made by mixture, as well as the classification and the separation of mixed material.