Recovery of valuable metals from mining and mineral processing waste

Ammonia-thiosulfate-copper leaching, aided by a direct current electrochemical impact, is proposed to extract gold (Au), silver (Ag) and copper (Cu) from old flotation tailings mixed with waste rock. Over 80 % of Au available in the waste material and over 75 % of Cu and Ag were extracted into the pregnant leach solution (PLS) at room temperature. Electrowinning from that PLS recovered around 92 % of Au and Cu, and about 87 % of Ag in the cathode deposit that is suitable for further metallurgical refining. The results are better, compared to leaching in the same system but without electrochemical impact and at air addition. The proposed direct current aided method is promising and more environmentally friendly compared to cyanide and even to sodium thiosulfate leaching.

ARC DISCHARGE SYNTHESIS OF CNTS IN HYDROGEN ENVIRONMENT IN PRESENCE OF MAGNETIC FIELD

In this study the effect of hydrogen ambient environment on the growth of carbon nanotubes by arc discharge plasma in presence of external magnetic field is investigated. The samples collected from cathode deposit are analyzed by field emission scanning electron microscopy and Raman spectroscopy. Results show an increase in carbon nanotube growth with increase in hydrogen ambient pressure. The magnetic field considerably enhances the growth of carbon nanotube as observed in FESEM micrographs. In Raman spectrum, high intensity of G peak as compared to D peak indicates the presence of high quality nanotubes. Magnetic effect remarkably decreases ID/IG ratio from 1.55 to 0.31 for ambient pressure 10 mbar.