F. A. López

The effect of the starting solution on the physico-chemical properties of zinc ferrite synthesized at low temperature

Abstract Fine particle zinc ferrite powders (ZnFe2O4) were synthesized by co-precipitation of a bi-ionic Fe3+/Zn2+ solution with 1 M n-butylamine at low temperature. Ferric nitrate and ferrous sulphate solutions were used as the starting material to investigate the effect of the source of iron on particle size, morphology, thermal behaviour and surface area of the final products. ZnFe2O4. In both cases, Zn2+ ions were provided by ZnO. The ferrous ions of the sulphate solution were previously oxidized with H2O2 in sulphuric medium. The cubic spinel-type structure of the ferrite product was obtained at a lower temperature when nitrate solution was used. Zinc ferrite of smaller particle size and higher surface area was obtained when ferrous sulphate was used as the starting solution. The ferrite precursors produced at room temperature and final products were characterized by X-ray powder diffraction, Fourier transformed infrared spectroscopy, thermal analyses, scanning and transmission electron microscopy and nitrogen adsorption volumetry.

Removal of copper ions from aqueous solutions by a steel-making by-product

A study is made of the use of a steel-making by-product (rolling mill scale) as a material for removing Cu(2+) ions from aqueous solutions. The influence of contact time, initial copper ion concentration and temperature on removal capability is considered. The removal of Cu(2+) ions from an aqueous solution involves two processes: on the one hand, the adsorption of Cu(2+) ions on the surface of mill scale due to the iron oxides present in the latter; and on the other hand, the cementation of Cu(2+) onto metallic iron contained in the mill scale. Rolling mill scale is seen to be an effective material for the removal of copper ions from aqueous solutions.

Characterisation of solid residues obtained on removal of Cr from waste water

Abstract This investigation was designed to characterise the solid residues obtained when waste water heavily contaminated with Cr 3+ is purified by the ‘ferrite precipitation method’ and to evaluate the efficiency of the process using different starting Fe 2+ /Cr 3+ ratios. In the case of Cr(VI) contamination, to avoid altering the proportions, the Cr 6+ was reduced to Cr 3+ in a preliminary step, and the same procedure applied. The solid compounds obtained were subjected to X-ray fluorescence and chemical analysis (inductively coupled plasma and potentiometric titrations). Findings suggest Cr x Fe 2+ Fe 3+ 2− x O 4 as the most probable stoichiometry of the products, where 0.09≤ x ≤0.59. X-ray diffractometry, differential scanning calorimetry and Fourier transform infrared patterns indicated a ‘normal spinel’ structure corresponding to ‘chromite-type’ chromium iron oxides. This structure differs considerably from that of divalent metal-bearing ferrites (‘inverse spinel’) and constitutes a new hydrothermal pathway for the generation of ‘non-stoichiometric chromites’. The following is proposed as the general oxide formation reaction: a Fe 2+ + x Cr 3+ + b OH − + c O 2 →Cr x Fe 3− x O 4 +Fe 2 O 3 . n H 2 O

Synthesis of mixed ferrite with spinel-type structure from a stainless steelmaking solid waste

Abstract Acid recovery plant powder, a solid by-product of the stainless steel industry with high iron, chromium and nickel content, was used to synthesise a nanocrystalline zinc–chromium–nickel ferrite in order to recover the total metal content of this waste as a valuable ferric product. Zn 2+ was provided by dissolving ZnO in HNO 3 and precipitation with 1M n -butylamine solution. The cubic spinel-type ferrite obtained, at temperature as low as 350°C, was characterised by X-ray powder diffraction, scanning and transmission electron microscopy.

Formation of metacinnabar by milling of liquid mercury and elemental sulfur for long term mercury storage.

In this paper we present the results of the formation of black HgS (metacinnabar) from liquid mercury and elemental sulfur using the mechanical energy provided by a ball mill in different conditions. Metacinnabar formation was observed even after short milling times (15 min) and unreacted liquid mercury was no longer detected after 60 min of milling. The reaction mechanism was monitored with a scanning electron microscope. The impact and friction forces of milling on the Hg and S mixture resulted in the formation of metacinnabar by reducing the size of mercury drops, giving rise to microspheres, and lowering the surface tension to allow sulfur grains to become adhered at the reaction interface. After 60 min of milling, the metacinnabar formation reaction was observed to be more than 99.99% complete, yielding a Toxicity Characteristic Leaching Procedure value of 3.1 microg/L Hg. The reaction product thus complies with the limits of the most stringent Universal Treatment Standard requirements, which allow a maximum TCLP concentration of 25 microg/L.

Transport of Au(CN)2 − by Mixtures of Amine Primene JMT and Phosphine Oxide Cyanex 923 Using the Pseudo-Emulsion Based Hollow-Fiber Strip Dispersion Technology

The transport of Au(CN)2 − between alkaline aqueous solutions and organic phases consisting of a mixture of the amine Primene JMT and the phosphine oxide Cyanex 923 in xylene was studied using the pseudo-emulsion based hollow-fiber strip dispersion (PEHFSD) technology. The feed phase was passed through the lumen side, and the pseudo-emulsions of the extractant mixtures and NaOH were passed through the shell side in a countercurrent mode using a single hollow-fiber contactor for extraction and stripping. In this membrane technology, the strippant (NaOH solution) is dispersed in the organic (Primene JMT + Cyanex 923 in xylene) membrane solution in a tank with an impeller stirrer adequate to form strip dispersion. The pseudo-emulsion phase is circulated from the reservoir tank to the membrane contactor to provide a constant supply of the organic solution to the membrane fibers. Furthermore, this technology allows a direct contact between the organic and strip solutions, providing a greater area for stripping and facilitating the metal recovery from the strip solution once both phases are separated. Various hydrodynamic and chemical parameters, such as flow of feed phase, extractant mixtures and gold concentrations, organic diluents, variation in feed pH, and the selectivity of the system with respect to the transport of different metal-cyano complexes, were investigated. Aqueous and membrane mass transfer coefficients were estimated for the present system.