David C. Shallcross

Ammonia Removal from Wastewaters Using Natural Australian Zeolite. I. Characterization of the Zeolite

This study considered the potential of a natural Australian zeolite, clinoptilolite, to remove ammonium from water. Ammonium-exchange capacity and rates of adsorption are critical to the assessment of the feasibility of the zeolite for application to continuous wastewater treatment. A laboratory study was undertaken, using pure solutions, to investigate the equilibria and kinetic characteristics of ammonium exchange in the zeolite. Binary equilibrium experiments provided information on the adsorption characteristics of the zeolite in terms of ammonia capacity at varying solution concentrations. These experiments also revealed that the highest ammonium removal efficiency was achieved when the zeolites exchange sites were converted to the sodium form. Multicomponent equilibrium experiments were carried out to determine the effects of competing cations on the ammonium-exchange capacity of the zeolite. The laboratory study indicated the zeolites selectivity for ammonium ions over other cations typically pre...

Ammonia Removal from Wastewaters Using Natural Australian Zeolite. II. Pilot-Scale Study Using Continuous Packed Column Process

A pilot-scale process was designed and operated to investigate the continuous removal of ammonia from sewage using natural zeolite from Australia. The process consisted of a fixed-bed ion-exchange system operated in the downflow mode. Evaluation of the pilot process was initially undertaken for ammonia removal from tap water spiked with ammonium chloride to provide performance data in the absence of competing cations. The performance of the pilot process was then assessed using sewage as feed. Breakthrough curves were constructed for a range of treatment flow rates. Existing models for packed bed performance were shown to be able to predict the breakthrough behavior of the process. The results of a study are presented that show that Australian natural zeolite, clinoptilolite, may be successfully employed in a fixed-bed ion-exchange process to achieve high ammonia removal efficiencies from aqueous solutions at rates commensurate with sand filtration. The rate of uptake of ammonium by the zeolite is sufficient to support a continuous high rate process.

Raman study on the speciation of copper cyanide complexes in highly saline solutions

Abstract Previous studies have established that the following three copper(I)-cyanide complexes form in aqueous solution: [Cu(CN) 2 ] − , [Cu(CN) 3 ] 2− and [Cu(CN) 4 ] 3− . The distribution of these complexes in solution at equilibrium is highly dependent upon the CN/Cu molar ratio. The speciation of copper cyanide complexes in highly saline solutions is of interest to Australian mining companies because of the unusually highly saline process water used on the goldfields of Western Australia (ca. 200 g/l total dissolved solids). This study has used the vibrational technique of Raman spectroscopy to determine the effect of highly saline water on the equilibrium distribution of copper cyanide complexes in solution for various CN/Cu molar ratios. For the first time it has been shown that in highly saline solutions the equilibrium distribution of copper cyanide complexes changes significantly. It has been established that [Cu(CN) 3 ] 2− predominantly forms in highly saline solutions for CN/Cu molar ratios of 2.2 to 2.5, where previously it has been shown that both [Cu(CN) 2 ] − and [Cu(CN) 3 ] 2− exist in non-saline solutions. Furthermore, in saline solutions containing an excess of cyanide (ca. 200 mg/l) only [Cu(CN) 4 ] 3− exists in solution and the formation of [Cu(CN) 3 ] 2− has not been observed. This phenomenon has been used to explain the increased selectivity of ion exchange resins for gold cyanide in highly saline solutions.

An improved model for the prediction of multicomponent ion exchange equilibria

Abstract Nonideal behaviour for liquid and resin phases is investigated theoretically and experimentally for ion exchange equilibrium of the aqueous ternary system Mg 2+ , Ca 2+ , Na + with Cl − . A semi-theoretical model is proposed in which the Pitzer approach is applied to the solution nonidealities, and the Wilson approach, based on experimental binary data, is applied to the resin. Predictions of the model agree with experimental data for both binary and ternary systems. The predictions of the proposed model are more accurate than those made using existing models.

Prediction of multicomponent ion exchange equilibria

A model has been developed for the prediction of multicomponent ion exchange equilibria which uses equilibrium data from binary systems to predict behaviour in multicomponent systems. Non-idealities in the solution phase are considered by applying Pitzers model for electrolyte behaviour while the resin phase activity coefficients are calculated by applying Wilsons model. In addition the equilibrium constants are obtained from the Gaines and Thomas approach and are independent of the resin phase activity coefficients. The model also considers the non-availability of some ions for exchange due to the formation of ion pairs in the solution phase. When applied to cation exchange in the binary and ternary systems involving H+, Na+, K+ and Ca2+ ions, the model predicts well the equilibrium behaviour. The equilibrium constant and the two binary interaction parameters are found to be independent of the conditions of the solution phase including concentration and the particular non-exchanging anionic species present in the solution.

Selective elution of copper and iron cyanide complexes from ion exchange resins using saline solutions

Abstract Numerous reagents for the elution of metal cyanide complexes from ion exchange resins have been proposed previously. However, a simple and cost-effective elution procedure has not been developed that is able to selectively strip metal cyanide complexes from the resin. The results of the current study show that highly saline solutions can be used to selectively elute copper cyanide and iron cyanide complexes from a variety of anion exchange resins containing different quaternary ammonium functional groups. It was found that for most resins an elution efficiency of greater than 80% copper and 99% iron was achieved within 12 bed volumes (BV) of a concentrated KCl or MgCl2 eluant containing 200 mg/L free cyanide. Gold cyanide and zinc cyanide complexes were not eluted from any of the resins studied. Poor elution of metal cyanide complexes was observed when a concentrated MgSO4 eluant containing 200 mg/L free cyanide was used. It is proposed that the chloride anion successfully competes with copper cyanide and iron cyanide complexes for active sites on the resin. Furthermore, the stereochemistry and degree of hydration of these complexes facilitate their selective elution by highly saline solutions. It is proposed that a highly saline elution stage followed by a conventional thiocyanate or zinc cyanide elution stage for strong base resins will produce a very simple and efficient elution procedure for the selective recovery of gold cyanide from strong base ion exchange resins. Furthermore, the selective elution procedure allows for the recycling of cyanide that is bound to the copper and iron cyanide complexes.

The effect of salinity on the capacity and selectivity of ion exchange resins for gold cyanide

Abstract Despite the success of several resin-in-pulp pilot plant operations in the Western World and large scale plants in the former Soviet Union the process of extracting gold from slurries using ion exchange resins is yet to gain recognition as a viable alternative to the carbon-in-pulp process. An experimental research program has investigated the potential use of anion exchange resins containing a variety of quaternary ammonium functional groups in highly saline process water such as that found in Western Australia. The effect of univalent and bivalent ions on gold adsorption has been studied. It was shown that the selectivity of the resin for gold cyanide was enhanced with increasing ionic strength. It has been proposed that the degree of hydration, polarisation and size of the adsorbing species are factors that contribute to the observed change in selectivity of the ion exchange resin at different salinity. It was observed that in highly saline solutions copper cyanide did not load significantly on any of the experimental resins studied. Furthermore, it has been shown that an existing commercial non-selective resin loads no significant amount of copper cyanide under saline conditions. It is proposed that the apparent change in selectivity of resins for gold cyanide is caused by anions that have a stronger affinity for the resin in these highly non-ideal solutions as well as a possible change in the distribution of copper cyanide complexes in solution. The results of this study demonstrate that the selectivity of ion exchange resins in highly saline water is significantly improved and as a consequence the resin-in-pulp process may be more efficient than carbon-in-pulp in process streams of high salinity.

Modifying In-Situ Combustion Performance by the Use of Water-Soluble Additives

This paper reports on experiments that were performed to study the effects of various additives on the oxidation kinetics of Californian and Venezuelan oils. Aqueous solutions of 10 metallic salts were mixed with sand and Huntington Beach, CA, oil. The mixtures were subjected to a constant flow of air and a linear heating schedule while the effluent gases were analyzed for composition. The variation in the oxygen consumption was analyzed with a model of three competing oxidation reactions. Values for the important kinetic parameters for the three reactions were obtained for each additive. Iron and tin salts were found to enhance fuel formation, while copper, nickel, and cadmium salts had no significant effects. Other experiments with a heavy Venezuelan oil showed that, contrary to earlier suggestions, the use of a ketal did not decrease fuel formation.

The speciation of gold and copper cyanide complexes on ion-exchange resins containing different functional groups

Abstract Despite the work of many researchers on the use of ion exchange technology for the recovery of gold from cyanide leached slurries, very little work has considered the effect that the chemical structure and hydrophilicity of the functional group may have on the speciation of the sorbed metal cyanide species. The present study investigated the properties of five resins that have the same type of resin matrix but contain a different aliphatic amino functional group. The tested resins include a variety of predominantly weak base resins that contain a small amount of strong base groups. These types of resin are similar to those that are currently being used in resin-in-pulp processes in the former Soviet Union for the recovery of gold (AM-2B). This study used CP/MAS 13 C-NMR to determine the chemical structure of the functional group on each synthesised resin. Raman spectroscopy was used in conjunction with FTIR spectroscopy to determine the speciation of copper(I)–cyanide and gold(I)–cyanide on each resin studied. Despite the equilibrium distribution of copper cyanide species in solution it was established that [Cu(CN) 3 ] 2− predominantly loaded onto all resins studied. However, for resins of a low ionic density the sorption of [Cu(CN) 2 ] − was also observed. Raman spectroscopy showed that gold cyanide loads onto each resin as the linear [Au(CN) 2 ] − complex and that no change in speciation was observed in highly saline solutions. The observed phenomena have been used to successfully explain the selective sorption properties of each resin in non-saline and highly saline solutions.

TERNARY AND QUATERNARY ION EXCHANGE EQUILIBRIA

ABSTRACT Using a semi-empirical model developed previously by the authors the cation exchange equilibria within the ternary H+ - Na+; - K+ system, and the quaternary H+ -Na+ - K+ - Ca++ system were investigated. Non-idealities in the solution phase are considered by applying Pitzers model for electrolyte behaviour while the resin phase activity coefficients are calculated by applying Wilsons model. Using the equilibrium constants and two binary interaction parameters determined experimentally for each of the constitutive binary systems, the equilibrium behaviour for the ternary and quaternary are predicted. The average deviations are all of smaller magnitude than the experimental error for the ternary and quaternary ion exchange systems studied.