Characterising the effect of microwave treatment on bio-leaching of coarse, massive sulphide ore particles

Charikinya, Edson (2015-12)

Thesis (PhD)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The aim of this work was to determine if microwave treatment of a typical massive sulphide ore, prior to bio-leaching would induce micro-cracks and enhance value mineral exposure resulting in improved bio-leaching metal extraction and kinetics. Using X-ray Computed tomography (XCT) and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) image analysis techniques, the degree of microwave induced damage, and the effect of this damage on mineral exposure, was quantified directly for the first time, in this study. Ore sample preparation was carried out using a primary jaw crusher followed by secondary crushing by either high pressure grinding rolls (HPGR) or a cone crusher. Particles investigated consisted of small (-5+4.75) mm, medium (-16+9.5) mm, and large (-25+19) mm HPGR and cone crushed particles. XCT and QEMSCAN results showed the presence of microwave induced cracks within the cone and HPGR crushed particles, treated at a microwave power density of 1× 109 W/m3 abs and exposure time 1.00 s. A qualitative analysis of the cracks, showed that the cracks consisted of both interphase trans-granular and grain boundary cracks. Both XCT and QEMSCAN analysis results showed that microwave treatment resulted in a significant increase of over 500% in crack volume for both modes of prior comminution at all particle sizes. Measurements of specific interfacial areas of particles before and after microwave treatment using XCT showed average losses in interfacial area of 31%, 23% and 16% for small (-5+4.75) mm, medium (-16+9.5) mm, and large (-25+19) mm particles. This demonstrated quantitatively for the first time, that microwave treatment of sulphide ores results in both grain boundary and trans-granular fracture. Value mineral grain exposure analysis was carried out on the XCT 3D data of particles before and after microwave treatment. The results showed an increase in the degree of sulphide grain exposure of 28%, 26% and 15% for small medium and large particles respectively. This is the first time that microwave particle damage and enhanced mineral exposure has been successfully quantified experimentally using XCT and image analysis techniques. Column leaching experiments to simulate heap bio-leaching environment, were carried out over 350 days to assess the downstream benefits of microwave treatment of heap leaching feed. The results showed that microwave pre-treatment of crushed ore for bio-leaching, will lead to improved leaching recovery. Improvements in overall Zn metal recoveries of 26%, 24% and 23% were observed for small (-5+4.75) mm, medium (-16+9.5) mm, and large (-25+19) mm microwave treated particles. The enhanced metal recovery seen for microwave treated material correlates well with the crack volume measurements and mineral exposure results. The column leaching results showed that medium (-16+9.5) mm sized microwave treated particles had a 10.1% higher metal recovery compared to small (-5+4.75) mm untreated particles. A comparison of overall metal recoveries of microwave treated cone and HPGR crushed ore particles showed that the mode of prior comminution gave no significant difference in recoveries at all sizes. This suggests that microwave treatment reduces the influence of mode of comminution on bio-leaching recovery. An investigation of the dissolution of sulphide grains in selected particles, using XCT 3D image analysis techniques over the course of 350 days of leaching, showed greater sub-surface conversion of minerals in microwave treated particles compared to untreated. Analysis of the cracks over the period of leaching using XCT data, showed a growth in microwave induced crack networks over 350 days of leaching. This suggest that microwave induced cracks accelerate reagent diffusion into the particles resulting in sub-surface conversion of minerals, during bio-leaching. A bonded particle model (BPM) was developed to simulate a multiphase massive sulphide ore approximating the ore used in the physical experimental investigations. The developed ore model consisted of pyrite, sphalerite and quartz phases which were identified as the major phases in the ore used in the experiment. The resulting microwave induced crack patterns for different model resolution were compared against those obtained from physical experiments. The results showed that model resolution has a significant effect on observed microwave induced crack damage and patterns. It was observed that cracks in models with different resolution propagate in a different pattern despite having the same macro-mechanical properties. Crack patterns obtained for higher models were observed to compare well with crack patterns observed from physical microwave treatment experiments. It can be concluded that model calibration using the usual simulated UCS and Brazilian tests alone is not adequate to fix the model resolution, for simulations of thermal induced cracks. These results show that model specimen resolution has a significant effect on observed micro crack damage and that the minimum base material “particle” size is not a free parameter. The effect of absorbent phase content on microwave induced damage was investigated for the first time using a high resolution model. Damage maps which show the percentage of micro-cracks as a function of power density and exposure time for different ternary ores and absorbent phase content were constructed. It has been shown that for the same power density and energy input, the fraction of micro-fractures induced by microwave treatment considerably depends on absorbent phase grain content.

AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om te bepaal of mikrogolfbehandeling van ʼn tipiese massiewe sulfiederts, voor biologing, mikrokrake sal induseer en die waarde van mineraalblootstelling sal verhoog, wat sal lei tot verbeterde biologing-metaalwinning en -kinetika. Met behulp van die beeldontledingstegnieke X-straal-berekende tomografie (XBT) en kwantitatiewe evaluering van minerale deur skanderingelektronmikroskopie (KEMSKAN) is die graad van mikrogolf-geïnduseerde skade, en die uitwerking van hierdie skade op mineraalblootstelling, direk vir die eerste keer in hierdie studie gekwantifiseer. Ertsmonstervoorbereiding is uitgevoer met behulp van primêre kakebrekermateriaal wat in twee dele verdeel is vir verdere vergruising deur óf ʼn hoëdrukmaalroller (HDMR) óf ʼn keëlbreker. Deeltjies wat ondersoek is, het bestaan uit klein (-5+4.75) mm, middelslag- (-16+9.5) mm en groot (-25+19) mm HDMR- en keël-vergruisde deeltjies. XBT- en KEMSKAN-resultate het gewys op die teenwoordigheid van mikrogolf-geïnduseerde krake in die HDMR- en keël-vergruisde deeltjies wat teen ʼn mikrogolfkragdigtheid van 1× 109 W/m3abs en blootstellingstyd 1.00 s behandel is. ʼn Kwalitatiewe analise van die krake het getoon dat die krake uit sowel interfasetranskorrel- as korrelgrenskrake bestaan. Die resultate van sowel die XBT- as die KEMSKANanalises het getoon dat mikrogolfbehandeling tot ʼn aanmerklike toename van meer as 500% in kraakvolume vir albei middele van voorvergruising van alle deeltjiegroottes lei. Metings van spesifieke tussenvlakoppervlaktes van deeltjies voor en ná mikrogolfbehandeling met XBT het gemiddelde verliese in tussenvlakoppervlakte van 31%, 23% en 16% vir klein (-5+4.75) mm, middelslag- (-16+9.5) mm en groot (-25+19) mm deeltjies getoon. Dit het kwantitatief vir die eerste keer getoon dat mikrogolfbehandeling van sulfiederts tot sowel korrelgrens- as transkorrel-frakture lei. ʼn Analise van die waarde van mineraalkorrelblootstelling is uitgevoer op die XBT 3D data van deeltjies voor en ná mikrogolfbehandeling. Die resultate het ʼn toename in die graad van sulfiedkorrelblootstelling van 28%, 26% en 15% vir onderskeidelik klein, middelslag- en groot deeltjies getoon. Dit is die eerste keer wat mikrogolfdeeltjieskade en versterkte mineraalblootstelling suksesvol eksperimenteel gekwantifiseer is met behulp van XBT- en beeldanalise-tegnieke. Kolomlogingseksperimente om ʼn stapelbiologingsomgewing te simuleer, is oor 350 dae uitgevoer om die stroomaf-voordele van mikrogolfbehandeling van stapellogingstoevoer te assesseer. Die resultate het getoon dat mikrogolf-voorbehandeling van vergruisde erts vir biologing tot verbeterde logingswinning sal lei. Verbeterings in algehele Zn-metaalwinnings van 26%, 24% en 23% is waargeneem vir klein (-5+4.75) mm, middelslag- (-16+9.5) mm en groot (-25+19) mm mikrogolfbehandelde deeltjies. Die verbeterde mineraalwinning vir mikrogolfbehandelde materiaal korreleer goed met die kraakvolumemetings- en mineraalblootstellingsresultate. Die kolomlogingsresultate het getoon dat die middelslaggrootte (-16+9.5) mm mikrogolfbehandelde deeltjies ʼn 10.1% hoër metaalwinning het in vergelyking met klein (-5+4.75) mm onbehandelde deeltjies. ʼn Vergelyking van algehele metaalwinning van mikrogolfbehandelde keël- en HPGRvergruisde ertsdeeltjies het getoon dat die middel van voorvergruising geen aanmerklike verandering in winning teen alle groottes meegebring het nie. Dit doen aan die hand dat mikrogolfbehandeling die invloed van middel van vergruising op biologingswinning verminder. ʼn Ondersoek na die oplossing van sulfiedkorrels in geselekteerde deeltjies, met behulp van XBT 3D beeldanalisetegnieke oor die verloop van 350 dae van loging, het groter suboppervlak-omsetting van minerale in mikrogolfbehandelde deeltjies getoon in vergelyking met onbehandelde deeltjies. ʼn Analise van die krake oor die logingstydperk met behulp van XBT-data het ʼn toename in mikrogolfgeïnduseerde kraaknetwerke oor 350 dae van loging getoon. Dit doen aan die hand dat mikrogolfgeïnduseerde krake reagensdiffusie in die deeltjies versnel, wat tot suboppervlak-omsetting van minerale tydens biologing lei. ʼn Gebonde deeltjiemodel is ontwikkel om ʼn veelfasige massiewe sulfiederts te simuleer wat soortgelyk is aan die erts wat in die fisiese eksperimente gebruik is. Die ontwikkelde ertsmodel het uit piriet-, sfaleriet- en kwarts-fases bestaan, wat geïdentifiseer is as die belangrikste fases in die erts wat in die eksperiment gebruik is. Die resultante mikrogolfgeïnduseerde kraakpatrone vir verskillende modelresolusies is met dié vergelyk wat uit die fisiese eksperimente verkry is. Die resultate het getoon dat die modelresolusie ʼn aanmerklike uitwerking op waargenome mikrogolfgeïnduseerde kraakskade en -patrone het. Daar is waargeneem dat krake in modelle met verskillende resolusies in verskillende patrone propageer, ten spyte daarvan dat hulle dieselfde makromeganiese eienskappe het. Kraakpatrone wat vir hoër modelle verkry is, het volgens waarneming goed vergelyk met kraakpatrone wat uit die fisiese mikrogolfbehandelingeksperimente waargeneem is. Die gevolgtrekking kan gemaak word dat modelkalibrasie met slegs die gewone gesimuleerde ODK- en Brasiliaanse toets nie genoegsaam is om die modelresolusie vir simulasies van termies geïnduseerde krake vas te stel nie. Hierdie resultate toon dat modelmonsterresolusie ʼn aanmerklike uitwerking op waargenome mikrokraakskade het en dat die minimumbasismateriaal se ‘deeltjie’-grootte nie ʼn vrye parameter is nie. Die uitwerking van absorbeerfase-inhoud op mikrogolfgeïnduseerde skade is vir die eerste keer met behulp van ʼn hoëresolusiemodel ondersoek. Skadekaarte wat die persentasie mikrokrake as ʼn funksie van kragdigtheid en blootstellingstyd vir verskillende ternêre ertse en absorbeerfase-inhoud toon, is saamgestel. Dit het getoon dat die fraksie mikrofrakture wat deur mikrogolfbehandeling geïnduseer is vir dieselfde kragdigtheid en energie-inset van absorbeerfase-korrelinhoud afhang.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98103
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