According to Harris Process, tellurium, arsenic, tin and antimony can be removed from the lead bullion with molten sodium hydroxide, sodium nitrate being used as an oxidizing agent, and transferred into the alkaline salt melt. The equipment used is the so-called “Harris Cylinder”. Its performance naturally depends on the operating conditions of a given plant (assay of the lead input, pump efficiency, surfaces of the reacting phases, retention time etc.). The separation of the impurities removed through the salt melts is accomplished by a combined metallurgical and hydrometallurgical process.(Excerpt from Extractive Metallurgy of Lead and Zinc)