Rolf Arne Kleiv

Using tailings as heavy metal adsorbents — The effect of buffering capacity

Abstract Previous studies have shown that silicate tailings could be used to treat heavy metal polluted water and to stabilise heavy metals in waste deposits and contaminated sediments. Adsorption to particle surfaces and hydroxide precipitation are thought to be the principal immobilisation mechanisms. To achieve optimal adsorption it is often necessary to increase the pH of the system. When using adsorbents possessing a capacity to neutralise acid, the pH increase could be achieved automatically and without any addition of chemicals. In this study the copper adsorption characteristics and buffering capacities of dust from the crushing and milling of nepheline syenite were investigated. The results were compared with the performance of a glacimarine clay, and showed that the nepheline syenite dust had superior buffer capacities and a superior ability to adsorb copper when exposed to initially acidic solutions. The results also indicated that chemisorption takes place on the nepheline syenite material, while adsorption on the clay is of a physical nature.

Modelling copper adsorption on olivine process dust using a simple linear multivariable regression model

Abstract This paper investigates the adsorption of copper on process dust from the production of olivine aggregates as a function of pH and the concentration of copper in solution. The olivine process dust, containing more than 90% forsterite, was retrieved from the dust removal system at A/S Olivin’s processing plant at Aheim in western Norway. Following characterisation of the material, batch adsorption experiments were conducted at 25 °C at an ionic strength of 0.05 M using a fixed adsorbent dose of 10 g/l and initial copper concentrations ([Cu]i) ranging from 20 to 600 μM (i.e. 1.27–38.1 mg/l). The final pH in solution (pHf) was varied from approximately 4 to 6. The obtained results show that the olivine process dust is capable of greatly reducing the concentration of copper in solution, even when exposed to relatively high initial copper concentrations. A linear multivariable regression model (LMVR model) was fitted to the logarithmically transformed experimental data. The good fit of the LMVR makes it possible to estimate retention as a function of pHf and the final copper concentration ([Cu]f), or, alternatively, [Cu]f as a function of pHf and [Cu]i. From an environmental engineering point of view, the latter would often be of greater interest since the success criteria usually are related to the resulting concentrations in solution.

Value enhancement of olivine process dust through air classification

As a result of the production of dry olivine sand products at A/S Olivin’s production plant at Åheim in western Norway, an annual quantity of some 20000–30000 t of process dust is produced. The bulk of this material is currently being sold as a slag conditioner at a relatively low price; hence, alternative uses of the process dust are now being sought. Information regarding the chemical composition of the material as a function of particle size facilitates product modifications through exclusion or mixing of individual size fractions. This paper demonstrates how such information can be obtained from air classification experiments when these are combined with chemical analysis of the produced size fractions. The classification and subsequent analysis of the olivine process dust revealed that the finer size fractions had high loss on ignition (LOI) values and were relatively low in MgO when compared with the bulk analysis. Removal of the finer fractions resulted in a remaining coarse product of significantly higher quality. The coarse material could be used as a raw material for further processing; it could be recycled or it could constitute a new product in itself.

Flotation of Metallurgical Grade Silicon and Silicon Metal from Slag by Selective Hydrogen Fluoride-Assisted Flotation

Flotation experiments performed on metallurgical grade silicon have demonstrated that silicon (Si) can be floated in diluted solutions of hydrogen fluoride (HF) and a frother. The recovery was found to depend on HF conditioning time, frother type, and the concentration of both HF and frother. Although Brij 58 produced the highest recoveries of the frothers that was tested, good recoveries were also obtained for Flotanol C07. Chemical analyses showed that the flotation products were purer than the corresponding feed materials, and that most impurity elements were concentrated in the tailings. A case study on cleaning of slag containing 36 pct metallurgical silicon showed promising results concerning the recovery of silicon by flotation.