Obtaining of Nano Gold from Concentrate (Banská Hodruša, Slovakia) Using Algae with Utilization of Mechanochemical Activation
The difficult and predominantly toxic processing of sulphide concentrates with a low gold content has prompted the finding of a more efficient and environmentally friendly method of obtaining this noble metal. This work was therefore focused on the recovery of gold from the concentrate of refractory sulphide complex (Banská Hodruša, Slovakia) using a non-cyanide mechanochemico-biological process. Gold in this complex concentrate is physically located in the intercrystalline space of sulfide minerals and fills in structural defects in sulfides. The precipitation of gold from the complex mineral matrices of the concentrate can be achieved using a mechanochemico-biological process. This innovative process makes it possible to recover gold by applying a thiourea solution, which is a preferred alternative to toxic a cyanidation. The use of a biological process with the application of algae has shown that algae with siliceous structures make it possible to obtain gold from a complex concentrate (Banská Hodruša, Slovakia) with dimensions of the nano. Limnetic algae (diatoms, golden algae) are part of aquatic ecosystems and form the largest of biomass of all plants on Earth. Mechanochemicobiological process is a method that allows to obtain 100 nm gold nanoparticles from refractory sulphide concentrate (Banská Hodruša, Slovakia). The mechanochemical activation of this concentrate and the siliceous shells of limnetic algae strains (Dinobryon, Surirella) in thiourea solution caused changes in the physicochemical properties of gold minerals as well as in their components. These structural changes, under specific conditions, had a decisive influence on the precipitation of gold nanoparticles into the thiourea solution. The gold nanoparticles were then fixed in a cell matrix on mechanochemically activated algal shells. The reason for the fixation of the gold nanoparticles was the action of biomolecules, which secreted algal cells during activation, while again preventing the chemical effect of metal ions present in the solution. Gold nanoparticles were obtained from the concentrate after less than one hour by the described mechanochemico-biological process. In the case of mechanochemical activation of the concentrate, but without activation of defined algae, the exclusion of gold nanoparticles was not even during of six hours. That was the reason, the algae had to be activated by milling to obtain gold from this sulfide concentrate.
