In this research, it was evaluated the size of industrial silicon dioxide nanoparticles (NPs- SiO2), and their influence on mechanical properties such as compression resistance in samples of type 1 Portland cement after their incorporation (4% by weight) in the formation of mortars, according to ASTM C 109. Through the characterization performed by DR-X technique, it was observed that NPs-SiO2 showed an approximate size of 12,1nm ± 0,3nm besides their amorphous nature. Using TEM analysis, measured sizes were between 10 to 20 nm, whereas the hydrodynamic size measured by DLS technique was 11,6nm ± 0,7nm. Because of the addition of 4% wt. of NPs-SiO2 in samples of type 1 Portland cement, an increase of compressive strength of 20,82 kgf/cm2 was obtained after 28 days, compared with samples of type 1 Portland cement without addition of silica nanoparticles. 

Leaching of polymetallic sulfides is often challenging due to the complexity of these systems. The main issues are related to the formation of surface by-products or to the presence of different metals that require a greater consumption of chemicals compared to that needed to extract the target metal during leaching. This latter case is followed in the present work using X-ray photoelectron spectroscopy (XPS) during the leaching of a silver-containing polymetallic (Mn-Fe-Pb) sulfide under three different cyanidation procedures: (1) conventional leaching, (2) ultrasound-assisted leaching, and (3) leaching of a sample pretreated in alkaline media. In all cases, leaching results in the build-up of Pb compounds (oxides/hydroxides) on the surface of the minerals, suggesting a mechanism in which Pb is first leached by hydroxide and cyanide and later is re-adsorbed as an external layer on the m...