Grant C. Lukey

THE EFFECT OF COMPOSITION AND TEMPERATURE ON THE PROPERTIES OF FLY ASH- AND KAOLINITE -BASED GEOPOLYMERS

Fundamental research into the geopolymerisation process is increasing rapidly because of the potential commercial application of this technology. Despite this, however, very little work has been undertaken to determine the relationship between composition and temperature on the final chemical and physical properties of geopolymeric products derived from waste materials. The present study shows that the differences in reactivity of source materials, used during the synthesis of waste-based geopolymers, significantly affect the final properties of the geopolymeric material. It is proposed that these observed changes in material properties are due to the incomplete dissolution of the waste material. The water content, the fly ash/kaolinite ratio, as well as the type of metal silicate used have a substantial effect on the final properties of the geopolymer. In particular, the current work shows that the thermal history of the source materials, such as kaolinite, as well as the curing regime for the geopolymer are important factors that must be taken into consideration when designing a geopolymer product for a specific application.

The characterisation of source materials in fly ash-based geopolymers

In recent years geopolymers have emerged as novel materials having unique and highly desirable chemical and mechanical properties. The technology of geopolymerisation is gaining commercial interest because it has been demonstrated that, in certain cases, the properties of geopolymeric materials are superior to existing cementitious systems. Source materials used during the synthesis of geopolymers from industrial by-products such as fly ash have an important role in determining the final properties of the geopolymer matrix. It is proposed in the current work that this is caused by the fact that not all of the waste material is dissolved and, therefore, some of the original structures of waste particles remain intact, becoming part of the new geopolymer structure and serving to either weaken or strengthen the newly formed structure. The current work uses XRD and FTIR techniques to characterise fly ash obtained from different sources in order to gain a greater understanding of the effect of phase composition on the dissolution behaviour, reactivity, and final physical and mechanical properties of fly ash-based geopolymeric materials.

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.

A COMPARATIVE STUDY OF KAOLINITE VERSUS METAKAOLINITE IN FLY ASH BASED GEOPOLYMERS CONTAINING IMMOBILIZED METALS

Geopolymer technology has emerged as an effective solution for the stabilization of industrial by-products and the immobilization of heavy metals. It has been established that the nature of the source materials used during synthesis has a significant effect on the final chemical and physical properties of the geopolymeric matrix. In particular, it has been established that the partial dissolution of specific wastes serves to either weaken or strengthen the newly formed structure. Moreover, leaching tests have shown that the use of either kaolinite or calcined kaolinite (metakaolinite) in fly ash based geopolymers affects the propensity of the matrix to immobilize heavy metals. This observation has practical implications for the application of geopolymer technology to the capping of mine tailings ponds or the backfilling of mines. The differences in dissolution behavior and the effect on final properties of geopolymeric materials have been studied for the kaolinite and metakaolinite system, with a view of gaining a wider appreciation of the behavior of other systems that are more difficult to study.

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.

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.

The Effect of Functional Group Structure on the Elution of Metal Cyanide Complexes from Ion-Exchange Resins

Previous investigations have established that the thiocyanate anion and the zinc cyanide complex are suitable eluants for the simultaneous recovery of metal cyanide complexes from ion-exchange resins. However, the effect of the ionic density of the resin and the stereochemistry of the functional group on metal recovery has never been systematically studied. The present study investigated the elution properties of five experimental resins that have the same type of resin matrix but contain different aliphatic amino functional groups. It is shown that ammonium thiocyanate is not a suitable eluant because iron and zinc are not completely eluted from any of the resins studied. It has been proposed that this is due to the precipitation of Zn2[Fe(CN)6] and possibly Fe4[Fe(CN)6]3 within the resin pores. It has been established that potassium thiocyanate at a pH greater than 12 can be used to recover more than 80% of copper, zinc, and iron within the first 10 bed volumes of eluant for most resins. The recovery of gold from each resin using potassium thiocyanate has been shown to be considerably slower than that of other metals, with approximately 60% recovered after 20 bed volumes of eluant. It has been found that the length of the alkyl chain of the functional group does not significantly affect the elution of metal cyanide complexes from the resins studied using the thiocyanate eluant. The elution of metals from all resins has been found to be superior when using a 0.5 M zinc cyanide eluant at a temperature of 50°C. More than 90% of copper, silver and iron were recovered from most resins within 4 bed volumes of eluant. However, the recovery of gold using a zinc cyanide eluant is dependent upon the ionic density of the resin and also the stereochemistry of the attached functional group. The results of this study show that zinc cyanide is not a suitable eluant for gold-selective ion-exchange resins.

The dependence of sorbed copper and nickel cyanide speciation on ion exchange resin type

The present study investigates the influence of functional group structure and resin matrix on the speciation of copper and nickel cyanides sorbed onto two commercially available ion exchange resins. Batch experiments were performed using synthetic copper and nickel solutions containing 50 and 200 mg/L free cyanide, respectively. Despite the presence of Cu(CN)32− and Cu(CN)43− in solution, it has been found using Raman spectroscopy that the Imac HP555s resin, which has a polystyrene–divinylbenzene matrix, loads predominantly the Cu(CN)32− complex. In contrast, the polyacrylic resin, Amberlite IRA958, sorbed significant amounts of both Cu(CN)32− and Cu(CN)43−. It has been found that the speciation of nickel cyanide sorbed onto each resin was the same. A recently developed mathematical model based on statistical thermodynamic principles has been used as a tool to understand further the equilibrium sorption of copper and nickel cyanide complexes onto each resin studied. A higher sorption energy for nickel compared to copper has been observed for the sorption onto Imac HP555s. In contrast, the sorption energy for copper was found to be higher than for nickel for the polyacrylic resin, Amberlite IRA958. The values of the model parameters obtained were correlated with the chemical features of each complex in solution as well as sorbed onto the resins.

Equilibrium model for the selective sorption of gold cyanide on different ion-exchange functional groups

Abstract Ion exchange resins are still not used commercially for gold extraction from leached pulps despite the many advantages of ion exchange resins over activated carbon. This is a result of the poor understanding of the chemistry involved and a lack of a rigorous method of modelling, design and scale-up. The present study describes a theoretical model based on the principles of statistical thermodynamics as well as the Metropolis Monte Carlo (MMC) numerical method that has been proposed previously to describe multi-component sorption equilibria. An important aspect of this modelling approach is that it does not use any solely empirical parameters. All parameters used describe only a single characteristic of the sorption system. It is therefore possible to include fundamental information of the system in order to facilitate easier parameter estimation. The model explicitly describes in a mathematical form classical non-ideal sorption phenomena such as selectivity, irreversibility and interaction between sorbed species which previously have only been understood from a chemical viewpoint. The model has been used to successfully describe the multicomponent equilibrium sorption of gold cyanide and copper cyanide onto ion exchange resins containing different aliphatic amino groups. Consequently, by varying the surface properties and comparing the model predictions with experimental data, further insight has been gained into the sorption properties of ion exchange resins for metal cyanide complexes.