Preg-robbing of Gold by Carbonaceous Materials Encountered in Gold Processing

Processing of gold from refractory ores containing carbonaceous materials (CM) poses challenges due to the ability of the CM to preg-rob dissolved gold. Depending on the type and maturity of CM encountered, preg-robbing of aurocyanide ion can lead to reduction in gold recovery ranging from a few percentages to more than 50%. Knowledge on the type of CM present, and its capacity for gold adsorption is important in predicting pre-treatment methods that can deactivate the CM and reduce its ability to preg-rob. This paper, as part of an on-going work, presents results on the degree of adsorption by the various carbonaceous materials encountered in gold processing, and estimates the amount of aurocyanide complex preg-robbed by them. To do this, various weights of carbonaceous materials (wood chips, charcoal, barren carbon and fresh activated carbon) were contacted with gold solution for a given period of time. The percentages of gold adsorbed on the various carbons were determined, and the results showed an increasing trend of preg-robbing in favour of wood chips < charcoal < barren carbon < activated carbon. Of all the CMs, wood chips have not undergone any carbonisation and/or activation, and thus exhibited the lowest affinity. The adsorption capacities in grams of gold per tonne of carbon over a 24-hr period were 30-65 for wood chips, 320-370 for charcoal, 410-420 for barren carbon and 580-650 for activated carbon. The trend shows direct correlation with the activities and the degrees of graphitisation and maturity of the various carbonaceous materials. It is thus important to characterise carbonaceous gold ores to know the maturity of the CM present, which will inform on the pre-treatment processes required. Keywords: Preg-Robbing, Wood Chips, Charcoal, Activated Carbon

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Enzymatic Pre-Treatment of Carbonaceous Matter in Preg-Robbing Gold Ores: Effect of Ferrous Ion Additives

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.262.43 ◽

2017 ◽

Vol 262 ◽

pp. 43-47

Author(s):

Kojo T. Konadu ◽

Keiko Sasaki ◽

Kwadwo Osseo-Asare ◽

Takashi Kaneta

Keyword(s):

Hydrogen Peroxide ◽

Activated Carbon ◽

Aromatic Compounds ◽

Ferrous Ion ◽

Alkaline Solutions ◽

Carbonaceous Matter ◽

Gold Ores ◽

Refractory Gold Ores ◽

Refractory Gold ◽

Pre Treatment

The bio-treatment of double refractory gold ores (DRGO) to reduce preg-robbing needs to account for the heterogeneity of the ore so as to acquire a much more complete picture of the system. To this end, the effects of ferrous ion additives on the degradation of powdered activated carbon (PAC) by cell-free spent medium (CFSM) was studied. Au(CN)2- adsorption and Raman spectrometric results suggest that the ferrous salt could have possibly reacted with some biogenic hydrogen peroxide to aid in the degradation of PAC. The bio-treatment produced mixed solid residues containing some partially degraded aromatic compounds which were soluble in alkaline solutions. Ultimately, biodegradation of PAC using CFSM in the presence of 50 µM FeSO4.7H2O for 7 days followed by washing with 3 mM NaOH reduced Au(CN)2- uptake by 80%.

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Low-pressure membrane filtration with unconventional coagulation regimes

Water Science & Technology Water Supply ◽

10.2166/ws.2005.0032 ◽

2005 ◽

Vol 5 (5) ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

K.Y. Choi ◽

B.A. Dempsey

Keyword(s):

Activated Carbon ◽

Membrane Filtration ◽

Membrane Surface ◽

Cross Flow ◽

Chemical Cleaning ◽

Sand Filters ◽

Charge Neutralization ◽

Floc Size ◽

Filtration System ◽

Pre Treatment

The objective of the research was to evaluate in-line coagulation to improve performance during ultrafiltration (UF). In-line coagulation means use of coagulants without removal of coagulated solids prior to UF. Performance was evaluated by removal of contaminants (water quality) and by resistance to filtration and recovery of flux after hydraulic or chemical cleaning (water production). We hypothesized that coagulation conditions inappropriate for conventional treatment, in particular under-dosing conditions that produce particles that neither settle nor are removed in rapid sand filters, would be effective for in-line coagulation prior to UF. A variety of pre-treatment processes for UF have been investigated including coagulation, powdered activated carbon (PAC) or granular activated carbon (GAC), adsorption on iron oxides or other pre-formed settleable solid phases, or ozonation. Coagulation pre-treatment is often used for removal of fouling substances prior to NF or RO. It has been reported that effective conventional coagulation conditions produced larger particles and this reduced fouling during membrane filtration by reducing adsorption in membrane pores, increasing cake porosity, and increasing transport of foulants away from the membrane surface. However, aggregates produced under sweep floc conditions were more compressible than for charge neutralization conditions, resulting in compaction when the membrane filtration system was pressurized. It was known that the coagulated suspension under either charge-neutralization or sweep floc condition showed similar steady-state flux under the cross-flow microfiltration mode. Another report on the concept of critical floc size suggested that flocs need to reach a certain critical size before MF, otherwise membranes can be irreversibly clogged by the coagulant solids. The authors were motivated to study the effect of various coagulation conditions on the performance of a membrane filtration system.

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Practical Guide to Determine the Impact of Radon and Other Radionuclides on Water Treatment Processes

Water Science & Technology ◽

10.2166/wst.1992.0568 ◽

1992 ◽

Vol 26 (5-6) ◽

pp. 1255-1264

Author(s):

K. L. Martins

Keyword(s):

Activated Carbon ◽

Water Treatment ◽

Environmental Protection Agency ◽

Treatment Plant ◽

Water Treatment Plant ◽

Packed Tower ◽

Treatment Processes ◽

Radioactivity Exposure ◽

The Impact ◽

Percent Removal

During treatment of groundwater, radon is often coincidentally removed by processes typically used to remove volatile organic compounds (VOCs)-for example, processes such as liquid-phase granular activated carbon (LGAC) adsorption and air stripping with vapor-phase carbon (VGAC). The removal of radon from drinking water is a positive benefit for the water user; however, the accumulation of radon on activated carbon may cause radiologic hazards for the water treatment plant operators and the spent carbon may be considered a low-level radioactive waste. To date, most literature on radon removal by water treatment processes was based on bench- or residential-scale systems. This paper addresses the impact of radon on municipal and industrial-scale applications. Available data have been used todevelop graphical methods of estimating the radioactivity exposure rates to facility operators and determine the fate of spent carbon. This paper will allow the reader to determine the potential for impact of radon on the system design and operation as follows.Estimate the percent removal of radon from water by LGAC adsorbers and packed tower air strippers. Also, a method to estimate the percent removal of radon by VGAC used for air stripper off-gas will be provided.Estimate if your local radon levels are such that the safety guidelines, suggested by USEPA (United States Environmental Protection Agency), of 25 mR/yr (0.1 mR/day) for radioactivity exposure may or may not be exceeded.Estimate the disposal requirements of the waste carbon for LGAC systems and VGAC for air stripper “Off-Gas” systems. Options for dealing with high radon levels are presented.

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Comparative environmental impact evaluation using life cycle assessment approach: a case study of integrated membrane-filtration system for the treatment of aerobically-digested palm oil mill effluent

Sustainable Environment Research ◽

10.1186/s42834-021-00089-5 ◽

2021 ◽

Vol 31 (1) ◽

Author(s):

Yeit Haan Teow ◽

Meng Teck Chong ◽

Kah Chun Ho ◽

Abdul Wahab Mohammad

Keyword(s):

Activated Carbon ◽

Life Cycle ◽

Palm Oil ◽

Membrane Filtration ◽

Electricity Consumption ◽

Sand Filters ◽

Unit Operations ◽

Filtration System ◽

Pre Treatment ◽

Aerobically Digested

AbstractAiming to mitigate wastewater pollution arising from the palm oil industry, this university-industry research-and-development project focused on the integration of serial treatment processes, including the use of moving bed biofilm reactor (MBBR), pre-treatment with sand filters and activated carbon filters, and membrane technology for aerobically-digested palm oil mill effluent (POME) treatment. To assess the potential of this sustainable alternative practice in the industry, the developed technology was demonstrated in a pilot-scale facility: four combinations (Combinations I to IV) of unit operations were developed in an integrated membrane-filtration system. Combination I includes a MBBR, pre-treatment unit comprising sand filters and activated carbon filters, ultrafiltration (UF) membrane, and reverse osmosis (RO) membrane, while Combination II excludes MBBR, Combination III excludes UF membrane, and Combination IV excludes both MBBR and UF membrane. Life cycle assessment (LCA) was performed to evaluate potential environmental impacts arising from each combination while achieving the goal of obtaining recycled and reusable water from the aerobically-digested POME treatment. It is reported that electricity consumption is the predominant factor contributing to most of those categories (50–77%) as the emissions of carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides, and volatile mercury during the combustion of fossil fuels. Combination I in the integrated membrane-filtration system with all unit operations incurring high electricity consumption (52 MJ) contributed to the greatest environmental impact. Electricity consumption registers the highest impact towards all life cycle impact categories: 73% on climate change, 80% on terrestrial acidification, 51% on eutrophication, and 43% on human toxicity. Conversely, Combination IV is the most environmentally-friendly process, since it involves only two-unit operations – pre-treatment unit (comprising sand filters and activated carbon filters) and RO membrane unit – and thus incurs the least electricity consumption (41.6 MJ). The LCA offers insights into each combination of the operating process and facilitates both researchers and the industry towards sustainable production.

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TiO2-Powdered Activated Carbon (TiO2/PAC) for Removal and Photocatalytic Properties of 2-Methylisoborneol (2-MIB) in Water

Water ◽

10.3390/w13121622 ◽

2021 ◽

Vol 13 (12) ◽

pp. 1622

Author(s):

Xiao-Pin Guo ◽

Peng Zang ◽

Yong-Mei Li ◽

Dong-Su Bi

Keyword(s):

Activated Carbon ◽

Natural Organic Matter ◽

Uv Light ◽

Sol Gel ◽

Light Irradiation ◽

Nano Tio2 ◽

Uv Light Irradiation ◽

Adsorption Capacities ◽

Taste And Odor ◽

Composite Photocatalysts

2-methylisoborneol (2-MIB) is a common taste and odor compound caused by off-flavor secondary metabolites, which represents one of the greatest challenges for drinking water utilities worldwide. A TiO2-coated activated carbon (TiO2/PAC) has been synthesized using the sol-gel method. A new TiO2/PAC photocatalyst has been successfully employed in photodegradation of 2-MIB under UV light irradiation. In addition, the combined results of XRD, SEM-EDX, FTIR and UV-Vis suggested that the nano-TiO2 had been successfully loaded on the surface of PAC. Experimental results of 2-MIB removal indicated that the adsorption capacities of PAC for 2-MIB were higher than that of TiO2/PAC. However, in the natural organic matter (NOM) bearing water, the removal efficiency of 2-MIB by TiO2/PAC and PAC were 97.8% and 65.4%, respectively, under UV light irradiation. Moreover, it was shown that the presence of NOMs had a distinct effect on the removal of MIB by TiO2/PAC and PAC. In addition, a simplified equivalent background compound (SEBC) model could not only be used to describe the competitive adsorption of MIB and NOM, but also represent the photocatalytic process. In comparison to other related studies, there are a few novel composite photocatalysts that could efficiently and rapidly remove MIB by the combination of adsorption and photocatalysis.

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An effective approach for modifying carbonaceous materials with niobium single sites to improve their catalytic properties

Dalton Transactions ◽

10.1039/c5dt03007b ◽

2015 ◽

Vol 44 (46) ◽

pp. 19956-19965 ◽

Cited By ~ 6

Author(s):

A. S. Bozzi ◽

R. L. Lavall ◽

T. E. Souza ◽

M. C. Pereira ◽

P. P. de Souza ◽

...

Keyword(s):

Carbon Nanotubes ◽

Graphene Oxide ◽

Activated Carbon ◽

Carbon Materials ◽

Catalytic Properties ◽

Carbonaceous Materials ◽

Simple Route ◽

Catalytically Active

In this paper we show a very simple route for the incorporation of catalytically active niobium species on the surface of carbon materials, such as graphene oxide, carbon nanotubes and activated carbon.

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Increase the Microporosity and CO2 Adsorption of a Commercial Activated Carbon

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.749.17 ◽

2015 ◽

Vol 749 ◽

pp. 17-21 ◽

Cited By ~ 2

Author(s):

Joanna Sreńscek Nazzal ◽

Karolina Glonek ◽

Jacek Młodzik ◽

Urszula Narkiewicz ◽

Antoni W. Morawski ◽

...

Keyword(s):

Activated Carbon ◽

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Carbon Materials ◽

Micropore Volume ◽

Microporous Carbon ◽

Microporous Carbons ◽

Adsorption Capacities

Microporous carbons prepared from commercial activated carbon WG12 by KOH and/or ZnCl2 treatment were examined as adsorbents for CO2 capture. The micropore volume and specific surface area of the resulting carbons varied from 0.52 cm3/g (1374 m2/g) to 0.70 cm3/g (1800 m2/g), respectively. The obtained microporous carbon materials showed high CO2 adsorption capacities at 40 bar pressure reaching 16.4 mmol/g.

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Prospects and problems of sludge pre-treatment processes

Water Science & Technology ◽

10.2166/wst.2001.0598 ◽

2001 ◽

Vol 44 (10) ◽

pp. 121-128 ◽

Cited By ~ 98

Author(s):

J.A. Müller

Keyword(s):

Wastewater Treatment ◽

Phase Changes ◽

Ozone Treatment ◽

Thermal Methods ◽

Sludge Treatment ◽

Freeze Thaw ◽

Positive Effects ◽

Treatment Processes ◽

Stage Of Development ◽

Pre Treatment

Pre-treatment processes have been developed in order to improve subsequent sludge treatment and disposal. Disintegration of sludge solids in the aqueous phase changes the sludge structure and solubilizes organic matter. This paper provides an overview of the applications of wet disintegration in wastewater and sludge treatment. Applied disintegration techniques such as mechanical, thermal, chemical and biological methods are briefly described. The methods are compared regarding energy consumption, operational reliability and stage of development for application on wastewater treatment plants. Mechanical and thermal methods appear to be most suitable at this stage. The effects of pre-treatment on subsequent sludge treatment processes and the wastewater treatment are described. The performance of various methods is assessed. For the improvement of stabilization, mechanical and ozone treatment as well as thermal treatment perform best. Dewatering can be enhanced by thermal and freeze/thaw treatment. All methods show positive effects in the reduction of the number of pathogens. Pre-treatment leads to secondary effects like the generation of recalcitrant compounds and odor, which is mainly a problem of thermal and ozone treatment. The evaluation of capital and operational costs is difficult, because of the lack of full-scale experience. Especially thermal, freeze/thaw and biological treatments can be realized at low costs if the conditions are appropriate. Nevertheless, the economic efficiency has to be investigated critically for each individual application.

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Investigation and assessment of sludge pre-treatment processes

Water Science & Technology ◽

10.2166/wst.2004.0618 ◽

2004 ◽

Vol 49 (10) ◽

pp. 97-104 ◽

Cited By ~ 43

Author(s):

J.A. Müller ◽

A. Winter ◽

G. Strünkmann

Keyword(s):

Fine Particles ◽

Degradation Process ◽

Solid Content ◽

Ozone Treatment ◽

Treatment Processes ◽

Sludge Properties ◽

Pre Treatment ◽

The Cost ◽

Degree Of Degradation ◽

Cell Disintegration

The pre-treatment of sludges by disintegration will result in a number of changes in sludge properties. Floc destruction as well as cell disintegration will occur. This leads to an increase of soluble substances and fine particles. Furthermore, biochemical reactions may appear during or immediately after disintegration. The influence of disintegration of excess sludge on anaerobic digestion was studied in full scale. A stirred ball mill, an ultrasound disintegrator, a lysate centrifuge and ozone treatment were used. The results of the degradation process were compared to a reference system without pre-treatment. An enhancement of the degree of degradation of 7.4% to 20% was observed. The pollution of sludge water as well as the dewatering properties of the digested sludge were investigated. COD and ammonia in the sludge water were increased and a higher polymer demand was observed while the solid content after dewatering stayed almost unchanged. Based on these results the cost effectiveness has been assessed taking into account different conditions (size of WWTP, cost for disposal, etc.). Capital and energy costs are the main factors while the decrease in disposal costs due to the reduced amount of sludge is the main profit factor.

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Sustainable Conversion of Agriculture and Food Waste into Activated Carbons Devoted to Fluoride Removal from Drinking Water in Senegal

International Journal of Chemistry ◽

10.5539/ijc.v8n1p8 ◽

2015 ◽

Vol 8 (1) ◽

pp. 8 ◽

Cited By ~ 3

Author(s):

Mohamad M. Diémé ◽

Maxime Hervy ◽

Saïdou N. Diop ◽

Claire Gérente ◽

Audrey Villot ◽

...

Keyword(s):

Drinking Water ◽

Activated Carbon ◽

Activated Carbons ◽

Public Health Problem ◽

Calcium Content ◽

Fluoride Removal ◽

Carbonaceous Materials ◽

Water Steam ◽

Surface Areas ◽

Fluoride Adsorption

The objective of this study was to investigate the production of activated carbons (AC) from cashew shells, and millet stalks and their efficiency in fluoride retention. These agricultural residues are collected from Senegal. It is known that some regions of Sénégal, commonly called the groundnut basin, are affected by a public health problem caused by an excess of fluoride in drinking water used by these populations. The activated carbons were produced by a combined pyrolysis and activation with water steam; no other chemical compounds were added. Then, activated carbonaceous materials obtained from cashew shells and millet stalks were called CS-H2O and MS-H2O respectively. CS-H2O and MS-H2O show very good adsorbent features, and present carbon content ranges between 71 % and 86 %. The BET surface areas are 942 m² g-1 and 1234 m².g-1 for CS-H2O and MS-H2O respectively. A third activated carbon produced from food wastes and coagulation-flocculation sludge (FW/CFS-H2O) was produced in the same conditions. Carbon and calcium content of FW/CFS-H2O are 32.6 and 39.3 % respectively. The kinetics sorption were performed with all these activated carbons, then the pseudo-first equation was used to describe the kinetics sorption. Fluoride adsorption isotherms were performed with synthetic and natural water with the best activated carbon from kinetics sorption, Langmuir and Freundlich models were used to describe the experimental data. The results showed that carbonaceous materials obtained from CS-H2O and MS-H2O were weakly efficient for fluoride removal. With FW/CFS-H2O, the adsorption capacity is 28.48 mg.g-1 with r² = 0.99 with synthetic water.

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