THE TECHNIQUES

MINERALS PROCESSING

SOLUTION ASSAYS of the pulp can be used to model potentially interfering precipitates and adsorbing species that may have changed due to ROM or processing changes.

QEMSCAN or MLA is normally used for mineralogical analyses. but do not separate crystalline from amorphous phases, identify different mineral structures with the same composition (e.g. sphalerite, wurtzite) or different elemental substitution and are practically limited to >5 µm particles. In our approach, this data is compared with QUANTITATIVE RIETVELD XRD (crystalline phases) and bulk assay for complete information.

EDTA CHEMICAL EXTRACTION is used to identify changes in ore oxidation (e.g. oxidised zone, longer-term stockpiling) and the presence in solution of reactive metal ion species, particularly in flotation where Cu, Pb, Ag are likely to induce inadvertent activation of gangue minerals after collector addition.

SCANNNING ELECTRON MICROSCOPY in different imaging modes with energy dispersive spectroscopy analysis provides direct observation, not available from standard QEMSCAN or MLA imaging, of surface interference by attachment of hydrophilic particles.


Contrasting scale morphologies from Bayer plant heat exchangers.

X-RAY PHOTOELECTRON SPECTROSCOPY AND TIME OF FLIGHT SECONDARY ION MASS SPECTROMETRY
are now used to specifically define the chemical species (including reaction products, adsorbed species, activators, collectors) their spatial distributions and their statistical distributions on the same mineral between feed, concentrate and tail or between successive leach, digestion or precipitation samples.

ToF-SIMS image (250 × 250 µm) of (a) Ag, (b) Cu, (c) Zn, (d) S and (e) CN. (f) Graph of factor loadings for Principal Component 2 for this area of ToF-SIMS data showing clear statistical correlation of Ag to CN, as well as Cu, Zn and S, suggesting flotation depression of these value components (Figure 7 from Minerals 3(1):1-15, 2013, DOI: 10.3390/min3010001).

MICRO-DIFFRACTION AND SYNCHROTRON ANALYSIS combining mineral phase, composition and atomic structure can specifically locate REE and PGM elements in feeds and processing products for optimal recovery.


Acid Mine Drainage: Methods and Techniques

Classification of ARD wastes and improved control of the acid generation/time profile (and dissolved species) are the primary aims of ARD management. The central importance of mineralogical analysis of the waste materials has been firmly established from single mineral, mixed mineral and real waste samples including direct correlation of different mineral assemblages with lab and field test results. A comprehensive set of experimental methods is available for predicting the geochemical reaction characteristics of different waste rock samples and their acid forming (or non-acid forming) behaviour in the AMIRA ARD Test Handbook developed in our AMIRA project with EGi.

NET ACID PRODUCING POTENTIAL (NAPP) = maximum potential acidity (MPA) (i.e. %S) – acid neutralising capacity (ANC). Improved assessment using % reactive sulfide only (CRS test) and adjustment for pyrrhotite content.

NET ACID GENERATION (NAG) accelerated oxidation test: static, kinetic, sequential.

COLUMN LEACH TESTS (Kinetic)

TEST PADS (Kinetic) from 100s to 1000s of tonnes The ANC measured in short-term Sobek tests as part of NAPP provides an estimate of the neutralisation available at rates comparable or matched to the initial rates of acid production in an ARD waste. This ANC is primarily derived from carbonates but can include significant contributions from more reactive silicate minerals (e.g. chlorites, anorthite, orthosilicates) in the waste that continue after the carbonates are exhausted. A methodology for measurement of non-carbonate, long-term, steady state, stoichiometric neutralisation rates (ANRnc) from these mineral sources has been developed. This can be used to evaluate the approach to matching the reduced acid generation rate as described in our AMD attachment. The availability of suitable reactive silicate and other minerals in waste rock or adjacent rock can be assessed by QXRD and tested for application in dumping strategies or as covers on ex sting dumps (e.g. Savage River Project).