Fungal-Transformation of Surrogate Sulphides and Carbonaceous Matter in Refractory Gold Ores

Refractory gold ores contain metal sulphides that encapsulate gold and prevent its dissolution by cyanide, and carbonaceous matter (CM) that adsorbs (or preg-rob) gold cyanide complex during cyanidation. Pretreatment is therefore a necessary step to decompose the sulphides and liberate gold before cyanidation, and to deactivate CM and prevent it from adsorbing dissolved gold. To contribute to the pool of knowledge on the development of microbial-treatment techniques for refractory gold ores, this paper presents an overview of on-going research aimed at assessing the capability of the fungus, Phanerochaete chrysospo-rium, to degrade sulphides and CM. Pure pyrite and arsenopyrite, with initial sulphide sulphur content of 52% and 20% respec-tively, were used as surrogate for metal sulphides, whereas lignite, bituminous and anthracite coals were used to model the behavior of CM in refractory gold ores. The extent of biotransformation was primarily monitored by measuring sulphide sul-phur in the residual sulphidic materials, and by determining the preg-robbing effect of the treated CM. Within 21 days of treat-ment, there was 18% and 39% oxidation of sulphide sulphur in pyrite and arsenopyrite respectively. During the same period, preg-robbing effect of CM reduced by 70-95% in the order of lignite < bituminous < anthracite. Partial characterization of the treated anthracite using XRD confirmed reduction in the graphitic structure of carbon, whereas in the case of pyrite, there was a decline in the major sulphide peak after microbial pretreatment. The results indicate that the fungus biotransforms mainly by increasing the amorphous nature of the substrates through destruction of the ordered structure, followed by introduction of oxygen groups. The findings suggest a novel and technically viable alternative method for oxidative pretreatment of refractory gold ores

Foreign patents surge and technology spillovers in China (1985-2009): evidence from the patent and trade markets

The paper investigates the determinants of foreign patent surge and the effects of technology spillovers in China based on an industry-level sample of 19 countries and regions from 1985 to 2009. We explore two hypotheses to explain the increasing foreign propensity to patent and the effects of technology spillovers in China, the market covering hypotheses and competitive threat hypotheses. The results show strong support for the competitive threat hypothesis. However, the foreign patenting surge in China does not mean China has more access to outsource advanced technology; on the contrary the technology spillover from foreign countries in China is limited. The paper investigates the determinants of foreign patent surge and the effects of technology spillovers in China based on an industry-level sample of 19 countries and regions from 1985 to 2009. We explore two hypotheses to explain the increasing foreign propensity to patent and the effects of technology spillovers in China, the market covering hypotheses and competitive threat hypotheses. The results show strong support for the competitive threat hypothesis. However, the foreign patenting surge in China does not mean China has more access to outsource advanced technology; on the contrary the technology spillover from foreign countries in China is limited

Recycling Potential of Waste Di-Isobutyl-Ketone (DIBK) and Recovery of Residual Gold

Di-Isobutyl-Ketone (DIBK) has been commonly used in most mining and allied industries to extract gold from aqueous solutions for analytical purposes. In most cases a complexing agent, methyl tricapryl ammonium chloride otherwise called aliquat 336 is added to the DIBK to give a 1% volume by volume solution. The DIBK containing aliquat 336 is then used to extract gold from aqueous solutions for subsequent analysis using Atomic Absorption Spectrophotometry (AAS). After the AAS analysis the DIBK-aliquat solution containing gold is stored as waste since its disposal is often associated with environmental and health problems. This paper investigated the possibility of using distillation to recover gold contained in the waste generated in Ghana as well as the recycling potential of the distillate (regenerated DIBK). It was established that distillation of the waste DIBK yielded about 92% distillate leaving a residue of tar, which contained all the gold in the waste. Thermal oxidation of the residue followed by conventional cyanidation of the resulting ash led to gold recovery of 98.97% and the gold extraction efficiency of the regenerated DIBK compares very well with that of fresh DIBK

Boundary Applicability of the Ghana’s Oil Block Fiscal Regimes

AbstractAttractiveness of fiscal regime has become more important in oil and gas investment decision than the rather geological prospectivity of the province. The terms and conditions contained in the fiscal system influence the investor’s evaluation of project. As Ghana determines to benefit greatly from the exploitation of the oil and gas resources, a robust fiscal system attractive in all economical and technical conditions needs to be designed. Ghana has recently become one of the frontiers in the oil and gas industry following its commercial discoveries of hydrocarbons in Deepwater Tano-Cape Three Point, the Jubilee field. Ghana’s oil industry is very young and some of the basins are under exploration surveillances waiting for commercial discoveries. Ghana’s Jubilee field uses various terms and conditions in her fiscal arrangement to govern the upstream operations. For continuous realisation of economic benefits to the State as well as the contractor, it is important the applicability of Ghana’s fiscal regime at varying boundary conditions of oil price and field reserves are evaluated. Discounted cash flow economic model which considers the major uncertainties was developed to evaluate the economic implications of the Jubilee field fiscal regime. Different price scenarios and varying field sizes were taken through rigorous sensitivity analysis. It was determined that for all field sizes considered at oil prices above $40/bbl, contractor’s NPVs are positive. The project take statistics are averagely around 64$40/bbl where the State’s take statistic is above 80% and contractor’s take below 20%. The State receives Additional Oil Entitlement(AOE) only when the oil price is above $40/bbl and the AOE increases steadily with the oil price for all the various field sizes. In general, the Jubilee field fiscal regime is fairly attractive and flexible and ensures stable shares of economic rents between the State and the contractor as the profitability of the field increases. Keywords: Reserves, Fiscal Regime, Cash Flow, Take Statistics, Net Present Valu

Geometallurgical Studies on Gold Ore for Enhanced Comminution and Leaching

Many gold processing plants are experiencing challenges as mining pits are becoming deeper, rocks are getting harder and more complex polymetallic and refractory ores are being encountered. The variations in the characteristics of ores lead to deviations from the established parameters, and these affect gold extraction efficiency. This paper presents a study where geological characteristics of the ore types from some mining pits were used to ascertain the influence of ore blends on improving the performances of comminution and leaching circuits. To achieve this, mineralogical, comminution, gravity recoverable gold and leaching investigations were conducted on fresh and weathered ore samples and their blends. Mineralogical study showed that the main rock types associated with the mine pits were dolerite, phyllites, conglomerates and sandstone. The dominant minerals were quartz, plagioclase, with traces of pyrites. The Crushability Work Indices of the rocks were between 30 and 37 KWh/t, which are generally higher than the maximum design value of 31.9 kWh/t, and this situation will pose throughput challenges in that section. The Bond Ball Mill Work Indices of the blends tested were between 16.4 kWh/t and 9.6 kWh/t and a blend ratio of 85% fresh and 15% weathered was found to have a Bond Ball Work Index almost equal to the design value of 14 kWh/t. With gold assays of 2.5 g/t for dolerite, 2.1 g/t for phyllite, 3.7 g/t for sandstone and 3.4 g/t for conglomerate, the gravity recoverable gold was in the order of sandstone 36% > phyllite (31.5%) > dolerite (29.5%) > conglomerate (18%). The overall gold recoveries were in the sequence of conglomerate (95%), sandstone (94%), phyllite (92%) and dolerite (87%). This information could be utilised in developing a proactive plant operations strategies for an operating plant in order to ultimately manage the plant and enhance achievement of set targets. Keywords: Geometallurgy; Ore Blends; Characterisation; Communition Circuit Performance; Gold Recover

Evaluation of the Performance of Local Cements with Imported Class ‘G’ Cement for Oil Well Cementing Operations in Ghana

Portland cement is the most commonly used cement in the oil and gas industry and it accounts for about 99% of all primary cementing operations throughout the world. For Portland cement to qualify as oil well cement, the chemical and physical properties must meet the required standards of the American Petroleum Institute (API). This research evaluates the performance of three locally manufactured cement samples and imported class G cement sample for oil and gas well cementing operations in Ghana. The paper details results of API specification tests and the physical properties of the local cements with the imported class G cement. The results indicated that locally manufactured cements have the potential to be used for cementing oil and gas wells. However, further tests should be conducted to ascertain their stability under High Pressure, High Temperature (HPHT) conditions.Keywords: Compressive strength, Free fluid, Portland cement, Rheology, Thickening tim

Oxidation Behaviour and Bio-oxidation of Gold-bearing Sulphide Ores: Oxygen Capabilities and Challenges

The paper presents an overview of bio-oxidation of sulphidic refractory gold ores prior to gold cyanidation. This review discusses several factors, more importantly, oxygen requirements and oxygen limitations in biological oxidation of various sulphide minerals associated with gold ores. The availability of sufficient oxygen in bio-oxidation systems can speed up and enhance the oxidation of sulphide minerals, allowing the gold to be liberated for further extraction. However, oxygen supply and its low solubility in water have been the major limiting factors in bio-oxidation processes. More importantly, oxygen limitations are found to affect the rate of sulphide oxidation and the volume of materials that can be treated for gold leaching. First, the paper discusses the influence of dissolved oxygen on the oxidation behaviour of various sulphide minerals found in refractory gold ores or concentrates. Further discussed are the limiting factors in relation to dissolved oxygen during bio-oxidation of refractory gold ores. This review demonstrates that oxygen availability is a major challenge and therefore, oxygen enhancement techniques or strategies are vitally needed. As well, the review serves to inspire new research into efficient strategies to enhance oxygen availability

Fungal-Transformation of Surrogate Sulphides and Carbonaceous Matter in Refractory Gold Ores: Revisited

In the recovery of gold from refractory gold ores, pretreatment is required to decompose sulphides and liberate occluded gold before cyanidation, and to deactivate carbonaceous matter and prevent it from adsorbing dissolved gold. Until the past three decades, most commercial pretreatment processes had been by abiotic means. Biological pretreatment methods on commercial basis is therefore a recent phenomenon, and several researches are underway to assess the ability of different biological agents in the breakdown of sulphur and carbonaceous matter (CM) in gold ores. This paper, which is a revisit of an earlier one, presents an overview of on-going research aimed at assessing the capability of the fungus, Phanerochaete chrysosporium, to degrade sulphides and CM. Surrogate carbonaceous materials (lignite, bituminous and anthracite coals) and pure sulphides (pyrite and arsenopyrite) were used to model the behavior of CM and sulphides in refractory gold ores. To monitor the extent of biotransformation, preg-robbing test was conducted on the as-received and treated CM, and sulphide sulphur in the residual sulphidic materials was also determined. From an initial preg-robbing effect of 125 µg of gold per gram of CM, the ability of CM to preg-rob gold reduced by 70-95% in the order of lignite<bituminous <anthracite within 21 days of treatment, whereas there were 18% and 39% oxidation of sulphide sulphur in pyrite and arsenopyrite respectively. XRD examination of the treated anthracite confirmed reduction in the graphitic structure of carbon following fungal transformation. Similarly, there was a decline in the major sulphide peak after microbial pretreatment. The results indicate that the fungus biotransforms through destruction of the ordered structure, followed by introduction of oxygen groups. The amorphous nature, thus generated, inhibits the uptake of aurocyanide ions by CM, while enhancing the affinity of cyanide for the oxidised sulphide material in subsequent cyanidation treatment. The findings contribute to knowledge on novel and technically viable alternative methods for oxidative pretreatment of refractory gold ores. Keywords: Phanerochaete Chrysosporium, Carbonaceous Matter, Metal Sulphides, Biotransformatio

Detoxification of Cyanide Wastewater by Cyanotrophic Organisms: the case of Phanerochaete chrysosporium

Abstract Cyanide, a carbon-nitrogen radical, is a major building block in many industries including pharmaceuticals, petrochemical and gold processing. In the gold extraction industry, cyanide has been the universal lixiviant for over a century due to better understood process chemistry, among others. Industries that discharge cyanide-laden effluents are mandated to keep concentrations below 0.2 mg/L to prevent death by cyanide-intoxification, which occurs when cyanide binds to key iron-containing enzymes and prevent them from supplying oxygen-containing blood to the tissues. Techniques used to attenuate cyanide in wastewater can broadly be grouped into chemical, physical and biological methods.  In recent times, attention has been placed on biotechnological methods, which make use of cyanotrophic microorganisms to clean up cyanide-contaminated environments. This paper reports on studies set out to assess the ability of Phanerochaete chrysosporium to degrade cyanide under different conditions including changes in cyanide concentration, culture mass, time, closed system and open system. At the end of 24-hour contact in an open agitated system with initial pH of 11.5, a control experiment using 100 mg/L cyanide revealed a natural attenuation of 15% with pH decreasing to 9.88, while the best myco-detoxification of 85% was achieved by contacting 100 mg/L cyanide with 0.5 g culture mass, translating into degradation capacity of 17.2 mg/g (milligram of cyanide per gram of culture) with pH reducing to 8.4 in 24 hours. The degradation could be based on a number of mechanisms including hydrolysis to HCN, oxidation to cyanyl radical and cyanate due to natural attenuation through atmospheric contact, and secretion of organic acid, oxidative enzymes, and hydrogen peroxide by the fungus.   Keywords: Cyanotrophic Organism, Myco-Detoxification, Cyanide-Laden Effluents, p

Transforming the construction sector: an institutional complexity perspective

Purpose Government initiatives to improve construction have increasingly become more focused on introducing a repertoire of technologies to transform the sector. In the literature on construction industry transformation through policy-backed initiatives, how firms will respond to the demands to adopt and use innovative technologies and approaches is taken for granted, and there is scarcely any attention given to the institutional implications of transformation agenda. The purpose of this paper is to discuss these gaps and offer directions for future research. Design/methodology/approach Following a synthesis of literature on the UK’s industry transformation agenda, the authors use the concepts of institutional logics, arrangements, complexity and strategic responses to suggest seven research questions that are at the nexus of policy-backed transformation and institutional theory. Findings In this paper, the authors argue that increasing demands for the adoption and use of digital technologies, platforms, manufacturing approaches and other “industry-4.0”-related technologies will reconfigure existing logics and arrangements in the construction industry, creating a problem of institutional complexity for general contracting firms in particular. Originality/value The questions are relevant for our understanding of the nature of institutional complexities, change, strategic firm responses, field-level dynamics and implications for the construction industry in relation to the transformation agenda. This paper is positioned to spur future research towards exploring the consequences of industry transformation through the lens of institutional theory. This research forms part of the Centre for Digital Built Britain’s (CDBB) work at the University of Cambridge within the Construction Innovation Hub (CIH). The Construction Innovation Hub is funded by UK Research and Innovation through the Industrial Strategy Fund