Through Baidu Encyclopedia, cobalt belongs to the light metal, in the classification, the density of the metal is less than 4500 kg/m3 is known as light metal, such as aluminum, magnesium, potassium, sodium and so on. And the density is greater than 4500 kg / cubic meter of metal is called heavy metals, such as copper, nickel, cobalt, lead, zinc, tin and so on. Cobalt is a metallic element with the chemical symbol Co, atomic number 27 and has a silvery-white metallic luster. Cobalt has a wide range of industrial and medical applications and is used in the manufacture of batteries, electronic devices, high temperature alloys, cemented carbides, etc. In addition, cobalt is used in the manufacture of copper, nickel, lead, zinc and tin. In addition, cobalt is also used in the manufacture of medical equipment and instruments, such as pacemakers, artificial joints and so on. The toxicity of cobalt is low, but prolonged exposure to cobalt compounds or cobalt metal may have some health effects. Therefore, cobalt is not a heavy metal.