Francisco José Alguacil

Adsorption of antimony and arsenic from a copper electrorefining solution onto activated carbon

Removal of arsenic, antimony and bismuth impurities from copper electrolytes is a primary target in copper electrorefineries. The present work investigates the possibilities of carbon adsorption technology in the removal of arsenic and antimony from a real Chilean electrolyte. Various variables which affect the metal adsorption/desorption operations are studied.

Transport of chromium (VI) through a Cyanex 923–xylene flat-sheet supported liquid membrane

Abstract The present investigation deals with carrier-facilitated membrane transport of chromium (VI) from chloride media across a flat-sheet supported liquid membrane (FSSLM) using as organic reagent the phosphine oxide, Cyanex 923. The permeation of Cr (VI) has been studied under various experimental conditions: stirring speed of the source phase, initial metal and carrier concentrations, organic phase diluent, HCl concentration in the source phase, composition of the stripping phase and support characteristics. The mass transfer coefficient was calculated as 67 μm/s and the thickness of the aqueous boundary layer was calculated to be 15 μm. Chromium permeation and thus speciation across the membrane was also investigated, and the order found was: CrO 4 2− =Cr 2 O 7 2− >Cr 3+ .

The extraction of mineral acids by the phosphine oxide Cyanex 923

The distribution equilibria of mineral acids: H2SO4, H3PO4, HCI, HClO4 and HNO3 between aqueous solutions and organic solutions of the phosphine oxide Cyanex 923 in toluene or decane are described. Partition studies have shown that the organic diluent only slightly influences the acid extraction. The extraction mechanism can be related to the solvation of the acid and formation of the L · Hm+Xm−1 (m = 1, 2 or 3) species in the organic phase, where L is the extractant; only in the case of initial high HNO33 concentrations is the formation of the L · (HNO3)2 species apparent in this phase. The effect of temperature on the acid extraction is also evaluated.

Unipolar charging of nanometer aerosol particles in a corona ionizer

Abstract A corona ionizer for unipolar charging of nanometer-sized aerosol particles has been constructed and evaluated. Charging efficiency and particle deposition loss (electrostatic and diffusional) have been measured for particle mobility-equivalent diameters below 10 nm , at different aerosol flow rates, different corona polarity and voltages, and also at two different positions of the corona electrode tip. Even though electrostatic deposition of charged particles within the ionizer was relatively large at high corona voltages, charging efficiencies as high as about 30% for 10 nm particles could be achieved for positive and negative corona. This figure is almost one order of magnitude higher than that attainable with radioactive bipolar chargers, and similar to that recently reported for other types of unipolar chargers developed by several researchers.

Processing of residual gold (III) solutions via ion exchange

The processing of gold (III)-hydrochloric acid solutions by the anionic ion exchange Lewatit MP-64_resin has been investigated. The influence of several variables such as the temperature, the hydrochloric acid and metal concentrations in the aqueous solution and the variation of the amount of resin added has been studied. Moreover, a kinetic study performed in the uptake of gold (III) by Lewatit MP-64_shows that either the film-diffusion and the particle-diffusion models fit the adsorption process on the resin. Results obtained from batch experiments were applied to a continuous system using a vertical column. The loaded resin could be eluted by an acidic thiourea solution at 20°C. Various systems were investigated to precipitate gold from eluants, only the use of sodium borohydride allowed to accomplish the recovery of the metal from the pregnant solutions. Gold was recovered as fine particles, which were characterised by means of optical and scanning electron microscopy.

Gold extraction equilibrium in the system Cyanex 921-HClAu(III)

Abstract The partition of gold from hydrochloric acid solutions by the phosphine oxide Cyanex 921 has been studied. The extraction system is exothermic (ΔH° = −44.6 kJ/mol), the extraction being influenced by several variables. Maximum gold extraction is obtained in the HCl concentration range 5–7 M. Experimental data were analyzed numerically using the program LETAGROPDISTR. The results showed that the extraction can be explained assuming the formation of the species HAUCl4L (log K° = 1.99) and HAuCl4L2 (log K° = 6.68) in the organic phase, where L represents the organic extractant. From the experimental data the interaction coefficients for (AuCl4−1, H+) were estimated. Gold stripping is achieved effectively with water and the reaction is endothermic (ΔH°= 16.9 kJ/mol). Results on the extraction of HCl by Cyanex 921 are also presented.

Preconcentration and matrix separation of precious metals in geological and related materials using metalfix-chelamine resin prior to inductively coupled plasma mass spectrometry

Abstract A method for determining Au, Pt, Pd, Ir and Rh in ores and silicates and Fe-formation rocks is described. Sample decomposition was carried out with aqua regia and HF, followed by fusion of any insoluble residue with Na22O2 in a glassycarbon crucible. The precious metals were separated, in 1.2 mol dm−3 HCl media, from the matrix elements by ion-exchange, using a mini-column with tetraethylenepentamine (metalfix-chelamine) resin. The resin was destroyed with HNO3 and H2O2 in a high-pressure vessel assisted by microwave heating, and the precious elements were determined by flow-injection inductively coupled plasma mass spectrometry. The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. The limits of quantification (10 sdn − 1) calculated from a procedural blank sample solution were 4.0, 2.0, 1.5, 0.8 and 0.5 ng g−1 for Au, Pt, Pd, Ir and Rh, respectively. The accuracy of the proposed method was tested by determining these elements in SARM 7 platinum-ore reference material. For all the analytes, the relative standard deviation of the combined dissolution, separation and determination methods was below 3.5% (n = 6).

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.

Considerations about the recycling of EAF flue dusts as source for the recovery of valuable metals by hydrometallurgical processes

Abstract The present work takes an EAF flue dust to research its possibilities as resource from which to recover valuable base metals, principally zinc, by means of hydrometallurgical processes. At the same time this approach renders a recycle of the flue dust and thus decreases its environmental impact. The EAF flue dust is leached by different leaching reagents: acid, basic and complexing, and from the different pregnant solutions several approaches were proposed to obtain the most valuable metals contained in it. These approaches included the application of solvent extraction and other hydrometallurgical techniques.

The phosphine oxides Cyanex 923 and Cyanex 925 as extractants for gold(I) cyanide aqueous solutions

Abstract The behaviour of the phosphine oxides Cyanex 923 and Cyanex 925 in the recovery of gold(I) from cyanide solutions is described. Extractions are studied as a function of several variables such as temperature, diluent aromaticity, ionic strength and extractant concentration. Gold(I) stripping can be accomplished effectively with low aqueous ionic strength solutions and at high temperatures. From the experimental results it is seen that Me+-Au(CN)2−·3R3PO, where Me+=Li+ and R3PO=the phosphine oxide, is extracted into the organic phase. The extracted species is probably solvated by water.