title: Towards cleaner fertilisers; Solution ion-exchange methods for reducing cadmium levels in reactive phosphate rock

authors: Dyche, Timothy Adam

subjects: Fertiliser

abstract: The aim of this study was to characterise reactive phosphate rock (RPR); a form of rock phosphate which can be used directly as fertiliser, and investigate the potential to reduce cadmium levels in RPR by application of calcium ion solutions derived from waste mussel shells. 

Analytical techniques including ICP-MS, XRD, XRF, SEM-EDX, and FTIR were used in the characterisation of reactive phosphate rock, as provided by Terracare. These techniques allowed for changes to both the macro and trace element composition of reactive phosphate rock to be measured and monitored as it was subjected to a calcium ion solutions and variety of chemical and physical reaction conditions, with the aim of selectively extracting cadmium ions, by ion exchange with calcium, while leaving the general structure of RPR unchanged.

The solubility of phosphate ions in RPR was tested at varying pH, the intention being to determine the pH range of solutions that could be used for cadmium extraction while minimising phosphate losses.

Calcium ion solutions were applied to reactive phosphate rock under a range of different reaction conditions. Changes to calcium ion concentration, contact time, pH, temperature, microwave irradiation, use of different counter ions and addition of potential cadmium stabilising ligands were tested for their effects on reactive phosphate rock. Promising results were observed, with elevated levels of cadmium found in many extraction solutions. Calcium chloride solution of 1 mol L⁻¹ concentration was found to be the most effective at extracting cadmium from RPR.

Mussel shells were characterised by analytical methods including ICP-MS, XRD, XRF, UV-Vis, and FTIR. The effects of heating to temperatures between 300°C and 900°C to the physical and chemical properties of mussel shells were studied. Mussel shells were used as a basis for calcium ion solutions by dissolving crushed mussel shell in mineral acids. These shell solutions were compared with solutions of pure calcium salts for their effectiveness in extracting cadmium ions. 

Overall the results of this study indicate that it is possible for significant amounts of cadmium to exchange from RPR into calcium ion solutions with comparatively small phosphate losses. It appears that mussel shells could provide a suitable source of calcium ions for this purpose. Overall indications are that cadmium extraction from RPR by ion exchange with calcium ion solutions is a concept worthy of further research. If the preliminary results prove to be accurate then further developments have the potential to contribute to improved environmental outcomes for both the fertiliser and shellfish industries in New Zealand.

text: Towards cleaner fertilisers; Solution ion-exchange methods for reducing cadmium levels in reactive phosphate rock The aim of this study was to characterise reactive phosphate rock (RPR); a form of rock phosphate which can be used directly as fertiliser, and investigate the potential to reduce cadmium levels in RPR by application of calcium ion solutions derived from waste mussel shells. 

Analytical techniques including ICP-MS, XRD, XRF, SEM-EDX, and FTIR were used in the characterisation of reactive phosphate rock, as provided by Terracare. These techniques allowed for changes to both the macro and trace element composition of reactive phosphate rock to be measured and monitored as it was subjected to a calcium ion solutions and variety of chemical and physical reaction conditions, with the aim of selectively extracting cadmium ions, by ion exchange with calcium, while leaving the general structure of RPR unchanged.

The solubility of phosphate ions in RPR was tested at varying pH, the intention being to determine the pH range of solutions that could be used for cadmium extraction while minimising phosphate losses.

Calcium ion solutions were applied to reactive phosphate rock under a range of different reaction conditions. Changes to calcium ion concentration, contact time, pH, temperature, microwave irradiation, use of different counter ions and addition of potential cadmium stabilising ligands were tested for their effects on reactive phosphate rock. Promising results were observed, with elevated levels of cadmium found in many extraction solutions. Calcium chloride solution of 1 mol L⁻¹ concentration was found to be the most effective at extracting cadmium from RPR.

Mussel shells were characterised by analytical methods including ICP-MS, XRD, XRF, UV-Vis, and FTIR. The effects of heating to temperatures between 300°C and 900°C to the physical and chemical properties of mussel shells were studied. Mussel shells were used as a basis for calcium ion solutions by dissolving crushed mussel shell in mineral acids. These shell solutions were compared with solutions of pure calcium salts for their effectiveness in extracting cadmium ions. 

Overall the results of this study indicate that it is possible for significant amounts of cadmium to exchange from RPR into calcium ion solutions with comparatively small phosphate losses. It appears that mussel shells could provide a suitable source of calcium ions for this purpose. Overall indications are that cadmium extraction from RPR by ion exchange with calcium ion solutions is a concept worthy of further research. If the preliminary results prove to be accurate then further developments have the potential to contribute to improved environmental outcomes for both the fertiliser and shellfish industries in New Zealand.

year: 2022

title: Are geothermal streams important sites of nutrient uptake in an agricultural and urbanising landscape (Rotorua, New Zealand)?

authors: Hoellein, Timothy

subjects: ecosystem function

abstract: Increased nutrient loading and eutrophication are common problems for lakes globally (Carpenter et al., 1998; Smith & Schindler, 2009). New Zealand is no exception, where 30% of lakes >1 ha have very poor to extremely poor water quality (Van Bunnik et al., 2007). Many of the iconic lakes in the well-known, geothermally active Rotorua region of New Zealand exhibit the adverse affects of eutrophication, including harmful algal blooms, bottom water hypoxia, reduced clarity (Hamilton et al., 2010) and loss of aquatic biodiversity (Hamilton, 2004; Burns, Mcintosh & Scholes, 2009). These lakes are important to New Zealand both economically and culturally (Edgar, 2009).

text: Are geothermal streams important sites of nutrient uptake in an agricultural and urbanising landscape (Rotorua, New Zealand)? Increased nutrient loading and eutrophication are common problems for lakes globally (Carpenter et al., 1998; Smith & Schindler, 2009). New Zealand is no exception, where 30% of lakes >1 ha have very poor to extremely poor water quality (Van Bunnik et al., 2007). Many of the iconic lakes in the well-known, geothermally active Rotorua region of New Zealand exhibit the adverse affects of eutrophication, including harmful algal blooms, bottom water hypoxia, reduced clarity (Hamilton et al., 2010) and loss of aquatic biodiversity (Hamilton, 2004; Burns, Mcintosh & Scholes, 2009). These lakes are important to New Zealand both economically and culturally (Edgar, 2009).

year: 2012-01

title: AMS radiocarbon dating of Rattus Exulans bone from the Kokohuia Site (New Zealand)

authors: Higham, Thomas F.G.

abstract: We AMS radiocarbon dated rat bones (Pacific rat (Rattus exulans)) from the archaeological site of Kokohuia, in Northland, New Zealand. An initial series were up to 1200 years too old, but the reason for the offset remained obscure. We considered dietary foodwebs, post-depositional contamination and taphonomy as possible explanations. None provided robust answers. Finally, we identified a laboratory-related error, in which a small amount of old carbon derived from humectants (glycerin) used to moisten ultrafilters prior to the extraction of bone collagen, had become incorporated in the dated collagen. The glycerin humectant was present in amounts averaging 30-40 mg C per ultrafilter, which ordinarily is too small to significantly affect single dates obtained on bone collagen, but was significant in the case of small rat bones. Redating of bones from identical contexts produced a series of results which were within agreement with the age of the site as determined from other materials, including short-lived identified charcoal, and marine and estuarine shell. These results sound a warning for dating very small bone samples, and emphasise the need to consider all possible contaminants derived from laboratory preparation and chemical processing background. In addition, it emphasises the requirement for utilising standard samples of identical type (eg, bone, charcoal, wood etc) which range from young (1-2 half-lives) to background in age, as well as low and high sample mass, as QA laboratory checks on reproducibility (Bronk Ramsey et al., in press).

text: AMS radiocarbon dating of Rattus Exulans bone from the Kokohuia Site (New Zealand) We AMS radiocarbon dated rat bones (Pacific rat (Rattus exulans)) from the archaeological site of Kokohuia, in Northland, New Zealand. An initial series were up to 1200 years too old, but the reason for the offset remained obscure. We considered dietary foodwebs, post-depositional contamination and taphonomy as possible explanations. None provided robust answers. Finally, we identified a laboratory-related error, in which a small amount of old carbon derived from humectants (glycerin) used to moisten ultrafilters prior to the extraction of bone collagen, had become incorporated in the dated collagen. The glycerin humectant was present in amounts averaging 30-40 mg C per ultrafilter, which ordinarily is too small to significantly affect single dates obtained on bone collagen, but was significant in the case of small rat bones. Redating of bones from identical contexts produced a series of results which were within agreement with the age of the site as determined from other materials, including short-lived identified charcoal, and marine and estuarine shell. These results sound a warning for dating very small bone samples, and emphasise the need to consider all possible contaminants derived from laboratory preparation and chemical processing background. In addition, it emphasises the requirement for utilising standard samples of identical type (eg, bone, charcoal, wood etc) which range from young (1-2 half-lives) to background in age, as well as low and high sample mass, as QA laboratory checks on reproducibility (Bronk Ramsey et al., in press).

year: 2004