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A concentrate obtained from mining tailings containing mainly cassiterite and columbotantalite was reduced for the production of tin metal. The compounds CaCO 3 , Na 2 CO 3 , K 2 CO 3 , and borax were used as fluxes in the pyrometallurgical reduction smelting process, and graphite was employed as the reducing agent. The greatest recovery of Sn (>95%) was obtained when using CaCO 3 as the flux; the purity of Sn was 96%. A slag equivalent to 25% of the mass of the initial concentrate was produced during the recovery of the Sn. This contained 45% Nb 2 O 5 and Ta 2 O 5 , adding extra value to the mine tailings. The tin metal ingot was purified by electrorefining involving a tin and H 2 SO 4 electrolyte solution and a 101.9 A/m 2 current applied for 148 h. Under these conditions, 90 wt % of the Sn in the ingot was recovered at a purity of 99.97%.

In recent years, agro-industrial residues are focusing attention worldwide as a new source of pozzolans; in Brazil one of the wastes generated from agro-industrial activities comes from elephant grass that is cultivated as biomass for energy cogeneration. The goal of this paper is to analyze the influence of elephant grass, once activated at 700 C for 1 h in electric furnace, on the evolution of the hydration reaction as well as physical and mechanical properties in blended cement elaborated with 20% of elephant grass ash. For the present study, different instrumental techniques of characterization and methodologies (XRF, XRD, TG/DTG, mercury porosimetry, isothermal calorimetry and mechanical strength) were used. The results obtained in the present work show, that due to its high pozzolanic activity, the elephant grass ash activated at 700 C can be used as an alternative pozzolan in the blended cement manufacture. Additions of 20% of ash confirm the formation of CSH gels and hexagonal C 4 AH 13 as main products from hydration as well as pozzolanic reaction. The 20% ash blended cement showed lower heat evolution than OPC and similar to the 20% silica fume blended cement, a 12% of reduction of compressive strength and an important reduction of pore sizes below 50 nm.

Obtaining pozzolanic materials from recycling of industrial waste and byproducts is a priority action of environmental policy all over the world. This paper describes the effect of activation conditions on the reaction kinetics in calcined clay waste (CCW)/calcium hydroxide systems. The CCW used in this work shows excellent qualities for use as supplementary cementing material in the manufacture of commercial blended cements. This research work presents an exhaustive study about the kinetics of a pozzolanic reaction in this cementing system. The results obtained by different techniques (DTA/TG, X-ray diffraction, and SEM/EDAX) confirm that the activation conditions (in the range 7001-8001C and 2-5 h of retention) have a direct effect on the formation and evolution of hydrated phases. Low activation temperatures favor the CSH gels' formation, while at higher temperatures aluminates (C 4 AH 13 ) and aluminum silicate hydrates (C 4 ASH 8 , hydrotalcites) are predominant.

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