Miquel Rovira

Leaching behaviour of magnesium phosphate cements containing high quantities of heavy metals

Stabilization/solidification (S/S) is one of the most employed techniques for treating liquid wastes containing heavy metals. Magnesium potassium phosphate cements have been used in recent years as stabilizing agents with positive results. However, little information is available about the retention of the metals by magnesium potassium phosphate cements matrices with the exception of the results of compliance tests. In this work, several pastes were prepared by reaction between low grade MgO and KH(2)PO(4) in the presence of different heavy metal nitrate solutions (containing Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) or Zn(II)). In all cases, the initial metal content of the dissolution was 25 g dm(-3) and the oxide-phosphate ratio of the pastes was (50:50) in weight. Four different leaching tests were conducted on magnesium potassium phosphate cement pastes: simple batch test (EN 12457-2), equilibrium leaching test, availability test (NEN 7371) and acid neutralization capacity test (ANC). The metal leachate concentration was determined by means of ICP-MS. The stabilization of metals was successful in all cases, although the immobilizing system shows a better behaviour for Pb(II) and Cr(III) under acidic or neutral conditions.

Cloud-Point Extraction of Gold(lll) with Nonionic Surfactant—Fundamental Studies and Application to Gold Recovery from Printed Substrate

ABSTRACT An aqueous solution of a nonionic surfactant, polyoxyethylene nonyl phenyl ether, having an average of 7.5 oxyethylene units, provides an aqueous two-phase system that is surfactant-rich and surfactant-lean at ambient temperature. The system found use as a separation field. Au(III) was effectively partitioned into the small surfactant-rich phase from hydrochloric acid solutions; thus such operational factors as the concentrations of the surfactant, HCl, and NaCl were investigated. Partitioning of other heavy metals was depressed, and selective extraction of Au(III) could be attained. Such a cloud-point extraction technique has been applied to the recovery of gold from an aqua regia leaching solution of a printed substrate, and an overall process scheme, including stripping and reduction steps, was proposed. By introducing scrubbing stages using a dilute HCl solution, satisfactory recovery of gold with a high yield and purity from undesirable metals could be obtained.

Semi-dynamic leaching tests of nickel containing wastes stabilized/solidified with magnesium potassium phosphate cements.

Herein is presented a study on the long-term leaching behaviour of nickel containing wastes stabilized/solidified with magnesium potassium phosphate cements. Two different semi-dynamic leaching tests were carried out on monolithic materials: ANS 16.1 test with liquid-to-solid ratio (L/S) of 10 dm(3) kg(-1) and increasing renewal times, and ASTM C1308 test with liquid-to-solid ratio (L/S) of 100 dm(3) kg(-1) and constant renewal time of 1 day. ASTM C1308 provides a lower degree of saturation of the leachant with respect to the leached material. The effectiveness of magnesium potassium phosphate cements for the inertization of nickel was proved. XRD analyses showed the presence of bobierrite on the monoliths surface after the leaching test, which had not been detected prior to the leaching test. In addition, the calculated cumulative release of the main components of the stabilization matrix (Mg(2+), total P and K(+)) was represented versus time in logarithmic scale and it was determined if the leaching mechanism corresponds to diffusion. Potassium is released by diffusion, while total phosphorous and magnesium show dissolution. Magnesium release in ANS 16.1 is slowed down because of saturation of the leachant. Experimental results demonstrate the importance of L/S ratio and renewal times in semi-dynamic leaching tests.

Review of the dielectric properties of nanofiltration membranes and verification of the single oriented layer approximation.

The structuring of water at soft solid surfaces remains an area of great interest to colloid science as a whole and has many applications in relation to colloid stability, foams, and wetting films as well as being central to membrane separations. Quantitatively calculating the structural components of thin layers of water and the interaction forces of hydrated molecules with the surface of pores through a layer of water having modified structure is one of the most important challenges in the physics of surface phenomenon. In this paper these effects are reviewed and discussed in relation to the confines of a capillary pore. Membrane nanofiltration is extremely complex and is dependent on the micro-hydrodynamics and interfacial events occurring at the membrane surface and within the membrane nanopores. There is significant debate as to the exact nature of these complex phenomena and rejection is typically attributed to a combination of steric and electrical effects. The electrical effects are less well understood and in particular the contribution of dielectric exclusion. A review of the two competing descriptions of dielectric exclusion is presented along with the theories currently used in modelling this phenomena. A series of rejection experiments of 0.01 M salt solutions at the membrane isoelectric point has been performed for the NF270 and NF99HF membranes. The dielectric constants inside the nanopore are calculated and these values were consistent for three of the salts studied, indicating that a simplistic model based on Born theory is accurate enough for engineering calculations and that ion solvation is most likely to be the more appropriate dielectric exclusion mechanism for true nanofiltration membranes.

Modelling of mass transfer in facilitated supported liquid-membrane transport of palladium(II) using di-(2-ethylhexyl) thiophosphoric acid

The permeation of Pd(II) through supported liquid membranes (SLMs) impregnated with di-(2-ethylhexyl) thiophosphoric acid (DEHTPA) in kerosene has been investigated. A model is reported describing the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data are quantitatively explained by mathematical equations describing the rate of transport. Different rate-controlling processes take place as long as the metal transport occurs. High selectivity in the separation of Pd(II) against Fe(III), Pt(IV), Rh(III) and Zn(II) is achieved and the lifetime of the membranes is also studied.

Effect of heavy metals and water content on the strength of magnesium phosphate cements

In this paper the mechanical properties of magnesium potassium phosphate cements used for the Stabilization/Solidification (S/S) of galvanic wastes were investigated. Surrogate wastes (metal nitrate dissolutions) were employed containing Cd, Cr(III), Cu, Ni, Pb or Zn at a concentration of 25 g dm(-3) and different water-to-solid (W/S) ratios (0.3, 0.4, 0.5 and 0.6 dm(3)kg(-1)) have been employed. Cements were prepared by mixing hard burned magnesia of about 70% purity with potassium dihydrogen phosphate. Compressive strength and tensile strength of specimens were determined. In addition the volume of permeable voids was measured. It was found that when comparing pastes that the volume of permeable voids increases and mechanical strength decreases with the increase of water-to-solid ratio (W/S). Nevertheless pastes with the same material proportions containing different metals show different mechanical strength values. The hydration products were analyzed by XRD. With the increase of water content not previously reported hydration compound was detected: bobierrite.

Recovery of palladium(II) from hydrochloric acid solutions using impregnated resins containing Alamine 336

Abstract Impregnated resins containing Alamine 336 were prepared by direct adsorption of the extractant onto Amberlite XAD2 and physico–chemical characterization was performed. The kinetic and equilibrium extraction of Pd(II) from hydrochloric acid media as well as Pd(II) loading isotherms are reported. Pd(II) extraction by resins containing Alamine 336 could be explained by the formation of (R3NH+)2PdCl4−2 complexes in the resin phase.

IMPREGNATED RESINS CONTAINING DI-(2-ETHYLHEXYL) THIOPHOSPHORIC ACID FOR THE EXTRACTION OF PALLADIUM(II). I. PREPARATION AND STUDY OF THE RETENTION AND DISTRIBUTION OF THE EXTRACTANT ON THE RESIN.

ABSTRACT Solvent impregnated resins containing di-(2-ethylhexyl) thiophosphoric acid(DEHTPA) were prepared by direct adsorption of the extractant onto Amberlite XAD2 using a dry impregnation method. The impregnated resins were characterized by means of potentiometnc titrations and specific surface area measurements, and a new method to determine DEHTPA content in the resin based on surface area measurements, is proposed. The distribution of DEHTPA between the aqueous phase and the resin phase was studied, and the data obtained

Sorption of Antimony (V) onto Synthetic Goethite in Carbonate Medium

Abstract The sorption kinetics of antimony(V) on synthetic goethite is very fast compared to the sorption of other metals on goethite (e.g. arsenic and selenium) and depends on temperature, with an activation energy of 49±9 kJ · mol−1 in the temperature range 15–35°C. Sorption isotherms have been developed at different temperatures and ionic strength values. The results have been modelled using a Langmuir isotherm and there is not a considerable influence of neither the temperature in the range studied (15°C–35°C), nor the ionic strength (between 0.001 and 0.01 mol · dm−3). Sorption is very high at pH values lower than 8, at more alkaline pH, the sorption decreases with pH, as expected considering the Antimony(V) predominating complex in solution, Sb(OH)6 −. Triple‐layer model successfully describes the data obtained by assuming a bidentate edge‐sharing surface complex of antimonate on the surface of goethite.

RECOVERY AND SEPARATION OF PLATINUM GROUP METALS USING IMPREGNATED RESINS CONTAINING ALAMINE 336

ABSTRACT The kinetics and equilibrium extraction of pd(II) pt(IV) and RH (III) from hydrochloric acid media using impregnated resins containing Alamine 336 impregnated onto Amberlite XAD2 were studied and compared. While Rh( III) was hardly extracted, Pd( II) and Pt( IV) extraction could be explained by the formation of ( R3 NH+ )2 MCLn − 2 complexes: n= 4 for Pd( H) and n= 6 for Pt( TV) Stripping and concentration of the extracted PGMs were assayed with HC1, HC104 and thiourea. Straightforward metal separations were designed on the basis of the results obtained in the single metal experiments, and selective co-extraction of Pd( II) and Pt( TV) from Rh( III)at low HC1 concentrations, as well as partial separation between Pd( ll) and Pt( IV) at high acid concentrations, were achieved.