The metal dissolves in mineral acids but is unaffected by potassium hydroxide or boiling water. When heated in the presence of the halogens or sulfur, direct combination takes place. The Earth's crust contains on the average about 0.05 part per million indium by weight. The element does not occur uncombined nor in independent minerals but as a trace in many minerals, particularly those of zinc and lead, from which it is obtained as a by-product. Though found mainly in sphalerite, significant quantities of indium also are contained in ores of copper, lead and tin.
Indium enters the roaster as an element of zinc concentrates.
Indium is then recovered from the slag along with zinc and lead during slag fuming, and the fume containing the indium is retreated. From the lead bullion, indium is recovered in lead dross slag which is electrothermally reduced into lead, tin, antimony, and indium bullion. This process takes between six to eight weeks. Indium has the unusual property when molten of clinging to or wetting clean glass and other surfaces, which makes it valuable for producing hermetic seals between glass, metals, quartz, ceramics, and marble. In spite of our best efforts, the above list may not include all indium producing companies in Canada.