Acquirement of Gold from Concentrate (Pezinok, Slovakia) with Utilization of Algae in Mechanochemical Processes

Abstract

The deficiency of primary raw materials and the difficult processing of sulphide concentrates with low gold content, as well as the long-time use of the dangerous cyanide method, instigated to the search a more effective and environmentally conscious method of acquirement this noble metal. For this reason, this work was focused on gold obtaining from a refractory sulphide complex concentrate (Pezinok, Slovakia) with the application of the non-cyanide mechanochemico-biological process. Gold in this complex concentrate occurs physically enclosed in the intercrystalline space of sulphide minerals, and is also isomorphic and fills structure defects in sulphides. The exclusion of gold from such complex mineral matrices of the concentrate can be achieved by using a mechanochemico-biological process. This innovative process makes possible obtaining of gold using an application of a thiourea solution, which is a convenient alternative opposite to the toxic cyanidation method. The utilized of the biological process with the application of algae has shown that algae with siliceous structures make it possible to obtain of gold from a complex concentrate (Pezinok, Slovakia) with dimension in the nano range. These algae are part of aquatic ecosystems and, in addition, are being food for other animals, utilizing for fuel production and, more recently, they are the important raw material for the production of hydrogen, methane and some types of biofuels. Limnetic algae (diatoms, golden algae) have unique properties, they create the largest mass of biomass of all plants on Earth and at the same time they are able to move. The mechanochemico-biological process is a method that enables to obtain gold nanoparticles 100 nm from the refractory sulphide concentrate (Pezinok, Slovakia). Mechanochemical activation of this concentrate and silica shells of the limnetic algae of tribes (Dinobryon, Surirella) in thiourea solution caused changes in physico-chemical properties of the minerals of gold as well as in the constituents of the algae minerals. These structural changes had under specific conditions a decisive influence on the exclusion of gold nanoparticles to the thiourea solution. The gold nanoparticles had subsequently fixed in the cellular matrix on mechanochemical activated algae shells. The reason for the fixation of gold nanoparticles was the action of biomolecules that algal cells during activation secreted while they defend again the chemical effect of metal ions present in the solution. Nanoparticles of gold were acquirement from the concentrate after less than two hours by described mechanochemico-biological process. In the case of mechanochemical activation of the concentrate, but without the activation of defined algae, the exclusion of gold nanoparticles was not confirmed even after a triple activation time (six hours). Owing to, the algae had to be activated to recover of gold from this sulphide concentrate. It follows, the entire mechanochemico-biological process had to be followed.