Nestor Cezar Heck

Synthesis of ZVI Particles for Acid Mine Drainage Reactive Barriers: Experimental and Theoretical Evaluation

Acid mine drainage (AMD) is acid water generation due to chemical action of oxygen and atmospheric humidity on sulfide minerals - strongly associated with coal exploration. Permeable reactive barrier (PRB) is an alternative process to the treatment of groundwater contaminated by AMD. One of the first substances to be used in PRBs for groundwater remediation was zero-valent iron (ZVI). This reagent can be prepared with the help of sodium borohydride, NaBH 4 , and iron chloride. This work aimed to study the fundamentals for the synthesis of ZVI from Fe-Cl aqueous solutions and the immobilization of metal ions with ZVI with the assistance of a “computational thermodynamics” tool. A concise experimental evaluation covering the preparation of ZVI as well as the reduction of Cu, Ni, and Al ions followed the theoretical analysis.

Aplicação da ferramenta termodinâmica computacional na simulação da produção de aço inoxidável

This work, done with the application of computational thermodynamics, deals with the fundamental aspects of the stainless steel production in the steelmaking. The understanding of the thermodynamics equilibria that occur during the process contribute for the improvement of operating controls and the yield of chromium - a comparatively expensive material. The methodology consisted to use the databases and the Gibbs Energy minimization routine of the FactSage software to calculate equilibria involving the systems Fe-Cr-O and Fe-Cr-O-C-Ni. The calculated values for the O content in equilibrium with Cr are in good accord with the obtained results using equations and data from literature. About the critical Cr concentration, at which the equilibrium oxide changes from FeO·Cr2O3 to Cr2O3, the results from this work are in good agreement with that values well known from literature, but show discrepancy when compared with recent works. Moreover, some aspects over which the technology is based are highlighted - the vacuum and temperature effects during refining process.

EAFD GENERATION – TERMODINAMIC ANALISYS OF Fe-Zn-O-Cl-H-C SYSTEM

The steel production in mini mills generates several process residues, among them there is the electric arc furnace dust (EAFD). This residue has as main elements Fe, O, and Zn, being classified as hazardous by the presence of Pb and Cd. Thermodynamic studies related to the formation of mineral species containing Fe, O and Zn elements were carried on due to the influence of these compounds in hydrometallurgical EAFD recycling processes. In recent years, a rise in the chlorine content of this residue was observed, mainly motivated by the increased use of scrap with polymeric impurities containing this element. In this work, based on computational thermodynamics tool FactSage, a general overview of gaseous and minerals species (found in EAFD) formed by Fe, Zn, O, Cl, H and C is shown – representing the organic origin of chlorine. For this study, the PVC polymer was used as the chlorine carrier substance which contaminates the EAF load.

TUNDISH SLAG CAPACITY TO ABSORB INCLUSIONS WHEN USING CALCIUM ALUMINATE BASED COVERING MATERIAL COMBINED WITH RICE HULL ASH

Tundish is the last reactor where significant metallurgical operations can still be done. Calcium aluminate slags are able to positively contribute to metallurgy considering oxide separation, protection against reoxidation and preclusion of resulphurisation. However, these are poor insulators. When using low melting point slags it is necessary to use another covering material. The deviation from saturation can be used as a measure of absorption capacity. By utilizing computerized construction of ternary and quaternary diagrams it is possible to compare different slags and to find proper slag compositions with reasonable capacity to dissolve inclusions. Objective of the present technical contribution is to evaluate tundish slag capacity to absorb inclusions, considering a particular tundish industrial slag and the changes in its chemical composition during continuous casting of steel. It was observed that slag composition changed during the continuous casting process; this variation is possibly related to interaction between the CaO-Al2O3 liquid slag and the rice hull ash layer which is used above it. Computational thermodynamics was used to determine activity of alumina dissolved in liquid slag; it was observed that the variation in slag composition did not change slag capacity to absorb inclusions, since precipitation of Al2O3 solid phases is not predicted.

Effects of Te additions and stirring in the In segregation in Ga1-xInxSb alloys

The influence of tellurium in the indium segregation of Ga1-xInxSb:Te ingots obtained by the conventional vertical Bridgman method (CVBM), under stirred and non-stirred conditions, was investigated. Three Te-doped ingots and three no-doped ingots were unidirectionally solidified at a constant speed of 2.0 mm/hour, inside quartz ampoules, closed under argon, and with a conical tip. The furnace temperature was set for overheating between 73.5 - 93oC, and temperature gradients between 3.0 - 3.3oC/mm. The tellurium doped ingots showed a smaller number of grains and no cracks in the middle region of the ingots, right after the tip, in comparison with the no-doped ingots. Moreover, when comparing the stirred with the non-stirred ingots, the EDS experimental profile of indium in Te-doped synthetized without melt stirring ingot showed a better agreement with the Scheil-Gulliver equation than the stirred Te-doped ingots. The Te-doped ingots when stirring the melt during synthesis showed a more constant axial indium distribution, up to 85% of their lengths. The constant lattice estimated from TEM diffraction images are respectively 6.29 A for the non-doped sample and 6.17 A for the Te-doped sample. A qualitative account for the increase of the lattice parameter and the Hall measurements results is that the tellurium compensates for the native acceptor defects, contributing to the microstructural quality in the Ga1-xInxSb ingots.

Solidification Behaviour of Slags: The Single Hot Thermocouple Technique

Abstract With the Single Hot Thermocouple Technique the solidification behaviour of metallurgical slags has been studied, building TTT and CCT diagrams, with in situ observation for melting and solidification under various thermal conditions. Slags in the system CSTNA were studied, analysing the kinetics of crystals growth. Following findings are reported: (i) for the slag CS (%CaO/%SiO2 = 0.7) no crystal is observed during continuous cooling even to low cooling rates, but on the other hand intense crystallisation is obtained when increasing the temperature after reaching a particular range of lower temperatures; (ii) it was observed that the longer the duration of the superheating is, the longer the incubation times for a slag CST (41 %CaO, 29 %SiO2, 30 %TiO2) becomes; (iii) the addition of Na2O into the CST slag system shortens intensely the crystals incubation times at TTT diagrams to the range of seconds.