Response of low-grade gold ore to cyanidation and thiourea leaching

In this study, leaching tests were conducted on representative samples provided from Hamze-Qarnein gold deposit with grade of 0.8?ppm using cyanidation and thiourea leaching. Effective parameters including particle size, reagent concentration, oxidant concentration, pH, and dissolution time were examined in both cyanidation and acidic extraction with thiourea. Gold recovery and reagent consumptions (lime, cyanide, thiourea, ferric sulfate, and sulfuric acid) were measured under different leaching conditions. The results showed that cyanidation method was efficient with 95.21% gold recovery with following conditions: d₈₀?=?63?µm, pH 10.5, cyanide consumption of 1.23?kg/t, and 12?h cyanidation time. The acidic leaching using thiourea, required more chemical reagents and maximum gold recovery of 90.48% was achieved with thiourea consumption, leaching time, and pH equal to 13.32?kg/t, 5?h, and 1.7, respectively. According to the results, there was an interaction between ferric sulfate and thiourea concentrations and modeling of this process utilizing historical data design confirmed that the most effective parameter was the molar ratio of ferric sulfate to thiourea. Maximum recovery of gold obtained at molar ratio of 1/1. In addition, based on the experimental results, kinetics parameters of first-order reaction for gold dissolution were determined for cyanidation and thiourea leaching separately; therefore, for cyanidation, R_∞ and K were 95.59% and 0.59?h^?1 respectively, while R_∞ and K were in order of 78% and 0.87?h^?1 for acidic leaching using thiourea.     

Characterisation and management of incinerator wastes

Management of municipal and hospital wastes by means of incineration processes generates solid residues, such as bottom and fly ashes and air pollution control residues with high content of heavy metals, inorganic salts and other organic compounds. Characterisation of 24 ash samples, collected from four municipal solid waste incinerators (MSWI) and six hospital medical waste incinerators (HMWI) located in the Basque Country Region (Northern Spain), were carried out at the request of Spanish Regulations and European Economic Community guidelines.The ecotoxicity values, EC(50), of the TCLP leachates show a high variability ranging from 12,967 to 1,000,000mgl(-1) in MSWI samples and from 2917 to 333,150mgl(-1) in HMWI samples. Results from chemical characterisation of DIN 38414-S4 leachates show a high concentration of lead, sulphate and chloride in MSWI samples and chromium in HMWI samples.     

Activated carbons prepared from wood particleboard wastes: Characterisation and phenol adsorption capacities

The problems of valorisation of particleboard wastes on one hand, and contamination of aqueous effluents by phenolic compounds on the other hand, are simultaneously considered in this work. Preparation of activated carbons from a two steps thermo-chemical process, formerly designed for generating combustible gases, is suggested. The resultant carbonaceous residue is activated with steam at 800 °C. Depending on the preparation conditions, surface areas within the range 800–1300 m²/g are obtained, close to that of a commercial activated carbon (CAC) specially designed for water treatment and used as a reference material. The present work shows that particleboard waste-derived activated carbons (WAC) are efficient adsorbents for the removal of phenol from aqueous solutions, with maximum measured capacities close to 500 mg/g. However, most of times, the adsorption capacities are slightly lower than that of the commercial material in the same conditions, i.e., at equilibrium phenol concentrations below 300 ppm. Given the extremely low cost of activated carbons prepared from particleboard waste, it should not be a problem to use it in somewhat higher amounts than what is required with a more expensive commercial material. Phenol adsorption isotherms at 298 K were correctly fitted by various equations modelling type I and type II isotherms for CAC and WAC, respectively. Phenol adsorption isotherms of type II were justified by a 3-stages adsorption mechanism.     

Bioleaching of heavy metals from a low-grade mining ore using Aspergillus niger

The main concern of this study is to develop a feasible and economical technique to microbially recover metals from oxide low-grade ores. Owing to the significant quantities of metals that are embodied in low-grade ores and mining residues, these are potential viable sources of metals. In addition, they potentially endanger the environment, as the metals they contain may be released to the environment in hazardous form. Hence, mining industries are seeking an efficient, economic technique to handle these ores. Pyrometallurgical and hydrometallurgical techniques are either very expensive, energy intensive or have a negative impact on the environment. For these reasons, biohydrometallurgical techniques are coming into perspective. In this study, by employing Aspergillus niger, the feasibility of recovery of metals from a mining residue is shown. A. niger exhibits good potential in generating a variety of organic acids effective for metal solubilization. Organic acid effectiveness was enhanced when sulfuric acid was added to the medium. Different agricultural wastes such as potato peels were tested. In addition, different auxiliary processes were evaluated in order to either elevate the efficiency or reduce costs. Finally, maximum solubilization of 68%, 46% and 34% were achieved for copper, zinc and nickel, respectively. Also iron co-dissolution was minimized as only 7% removal occurred.     

Long-term field and laboratory leaching tests of cemented radioactive wastes

Experiments with real and simulated radioactive cementitious wasteforms were set up to compare the leaching behaviour of cementitious wasteforms containing nuclear power plant operational waste in field and laboratory test conditions. Experiments revealed that the average annual (137)Cs leach rate in deionised water was about thirty-five times greater compared with the measured average value for the 1st year of the field test. Cumulative leached fraction of (137)Cs for 1st year (3.74%) was close to values reported in literature for similar laboratory experiments in deionised water, however more than two orders of magnitude higher than the 1st year leached fraction of (137)Cs in the repository test (0.01%). Therefore, to compare field and laboratory test results, a scaling factor is required in order to account for surface to volume factor difference, multiplied by a temperature factor and a leach rate decrease coefficient related to the ground water composition.     

Characterisation and recovery of sodium chloride from salt-laden solid waste generated from leather industry

In this present investigation, physical and chemical characteristics of salt-laden solid waste (SLSW) generated from leather industry during soaking process of raw skins/hides and reverse osmosis reject stream were determined. The disposal of SLSW onto landfill was banned due to the possibility of ground water contamination by leachate, and its treatment process becomes tedious and cost intensive. The detailed characterisation of SLSW was evaluated for the development of effective methods for the treatment and/or disposal of SLSW. In the present study, sodium chloride was recovered to reduce the impact of the disposal of SLSW. The recovery of sodium chloride was achieved by selective precipitation using hydrogen chloride gas as a precipitating agent. The optimum conditions for the precipitation of sodium chloride were concentration of SLSW, 60 % (w/w); HCl gas purging, time 3 min (for a batch volume of 100 mL); pH, 8.0; and temperature, 30–40 °C. The scanning electron microscopy images of SLSW and the recovered sodium chloride were captured to observe the surface morphology. The recovered salt showed purity equivalent to that of standard reference salt. The recovered salt can be reused within leather sector or to the other process industries that meet their specification.     

Precipitation of cesium jointly with uranium from nitric acid liquid radioactive wastes to obtain solid matrices for long-term storage

The possibility of converting liquid radioactive wastes containing Cs into chemically and thermodynamically stable compounds, cesium uranates, was examined. Cesium uranate of the composition Cs₄U₅O₁₇ can be prepared by different procedures. The resulting compounds are characterized by fairly low Cs leaching rate, which will probably allow liquid cesium-containing radioactive wastes to be converted to solid matrices of small volume, ensuring long-term storage of cesium-containing wastes.     

Evaluating the applicability of a modified toxicity characteristic leaching procedure (TCLP) for the classification of cementitious wastes containing lead and cadmium

Having the toxicity characteristic leaching procedure (TCLP) as a starting point, this study examined the effect of the various leaching parameters on the leaching of Pb and Cd from cementitious wastes. Using modified TCLP procedures, the parameters investigated were the acid concentration, leaching duration, particle size of the crushed waste, liquid to solid ratio, and the acid type. The main finding was that the final leachate pH controls the leachability of metals due to its influence on their solubility. The high alkalinity of cementitious waste buffers the leachate at a pH where most metals become insoluble. The TCLP was found to result in an unrealistic condition for cementitious wastes due to the high resultant leachate pH.     

Mass transfer in the leaching of a solid from a porous sphere

We derive a sequence of approximate solutions of the problem of the kinetics of the extraction of a solid material uniformly filling the volume of a porous particle when it interacts with a liquid which selectively dissolves this material.     

Assessing the environmental footprints of the manganese recovery process from low-grade ore to synthesize manganese ferrite

Clean Technologies and Environmental Policy - Increasing demand for manganese and rapid depletion of high-grade manganese ores grow attention to other resources. However, environmental impacts and...     

低温酸浸高铁铝土矿中铁和铝的溶出规律研究

采用低温酸浸法对广西高铁铝土矿中的铝和铁的溶出规律进行了研究,考察了硫酸浓度、浸出温度、浸出时间及液固比因素对铝土矿中铝和铁溶出率的影响.结果表明,最优浸出条件为浸出时间60min,浸出温度100℃,液固比5∶1,硫酸浓度20％.此条件下铁的浸出率为98.68％,铝的浸出率为3.02％,溶出比为32.68,可实现高铁铝土矿中铁和铝的分步溶出.对该浸出过程进行动力学分析研究表明,此条件下浸出过程属化学反应控制,其控制动力学方程为:lgk=3-1.83×10-31/T反应活化能Ea=35.11kJ/mol.     

Development of sodium propionate-based deep eutectic solvents for polyphenol extraction from onion solid wastes

Clean Technologies and Environmental Policy - The objective of the study presented herein was the optimisation of onion solid waste (OSW) polyphenol extraction, using sodium propionate-based deep...     

Emission of volatile organic compounds from composting of different solid wastes: abatement by biofiltration

Emission of volatile organic compounds (VOCs) produced during composting of different organic wastes (source-selected organic fraction of municipal solid wastes (OFMSW), raw sludge (RS) and anaerobically digested wastewater sludge (ADS) and animal by-products (AP)) and its subsequent biofiltration have been studied. Composting was performed in a laboratory scale composting plant (30l) and the exhaust gases generated were treated by means of a compost biofilter. VOCs concentration in the composting exhaust gases for each composting process ranged from 50 to 695 mg C m-3 for OFMSW (5:1), from 13 to 190 mg C m-3 for OFMSW (1:1), from 200 to 965 mg C m-3 for RS, from 43 to 2900 mg C m-3 for ADS and from 50 to 465 mg C m-3 for AP. VOCs emissions were higher during the beginning of the composting process and were not generally related to the biological activity of the process. These emissions corresponded to an average loading rate applied to the biofilter from 2.56 to 29.7 g C m-3 biofilter h-1. VOCs concentration in the exhaust gas from the biofilter ranged from 55 to 295 mg C m-3 for OFMSW (5:1), from 12 to 145 mg C m-3 for OFMSW (1:1), from 55 to 270 mg C m-3 for RS, from 42 to 855 mg C m-3 for ADS and from 55 to 315 mg C m-3 for AP. Removal efficiencies up to 97% were achieved although they were highly dependent of the composted waste. An important observation was that the compost biofilter emitted VOCs with an estimated concentration of 50 mg C m-3.     

Kinetics of sulfuric acid leaching of cadmium from Cd-Ni zinc plant residues

Cd-Ni filtercakes are produced continuously at the third purification step in the electrolytic production of zinc in the National Iranian Lead and Zinc Company (NILZ) in northwestern Iran. In this research, the dissolution kinetics of cadmium from Cd-Ni residues produced in NILZ plant has been investigated. Hence, the effects of temperature, sulfuric acid concentration, particle size and stirring speed on the kinetics of cadmium dissolution in sulfuric acid were studied. The dissolution kinetics at 25-55 degrees C and t相似文献   

Pollution prevention in the semiconductor industry through recovery and recycling of gallium and arsenic from gaas solid wastes

 A process has been developed for the on-site recovery of both arsenic and gallium from gallium arsenide (GaAs) solid wastes. Until the present, very little effort has been made to attempt to recycle any but the largest-sized pieces of such wastes back into the crystal-growing process. Even when recovery is attempted, all of the effort has been focused on the high-value gallium and no efforts have been made for recovery and reuse of the toxic constituent arsenic. The process described herein first involves the thermal separation of GaAs solid wastes into their constituent elements (with a minimum of energy input or additional handling). Each of the separated elements is then purified to the required levels for further crystal growth using low-cost procedures. Because of this three step approach, the developed procedure can accommodate a wide range of input material characteristics. Prior work with GaAs thermal separation and constituent element purification provided a template for the development of this process, and subsequent thermodynamic consideration of each of these unit operations provided a theoretical basis for process optimization. A patent application for the developed process has been submitted to the United States Patent Office. This paper details the development of the thermal separation process, with important design specifications. Received: 11 July 1999 / Accepted: 4 August 1999     

Influence of leachate recirculation on aerobic and anaerobic decomposition of solid wastes

In this study, the effect of leachate recirculation on aerobic and anaerobic degradation of municipal solid wastes is determined by four laboratory-scale landfill reactors. The options studied and compared with the traditional anaerobic landfill are: leachate recirculation, landfill aeration, and aeration with leachate recirculation. Leachate quality is regularly monitored by the means of pH, alkalinity, total dissolved solids, conductivity, oxidation-reduction potential, chloride, chemical oxygen demand, ammonia, and total Kjeldahl nitrogen, in addition to generated leachate quantity. Aerobic leachate recirculated landfill appears to be the most effective option in the removal of organic matter and ammonia. The main difference between aerobic recirculated and non-recirculated landfill options is determined at leachate quantity. Recirculation is more effective on anaerobic degradation of solid waste than aerobic degradation. Further studies are going on to determine the optimum operational conditions for aeration and leachate recirculation rates, also with the operational costs of aeration and recirculation.     

Characterisation of the structure and thermophysical properties of solid electroslag remelting slags

The solid structure and thermophysical properties of three electroslag remelting (ESR) slags were characterised. Samples from ESR trials performed by Special Metals Corporation in Burnaugh, KY, were compared to samples solidified in a vacuum induction melter. The microstructures were characterised using a combination of optical and electron microscopy, X-ray diffraction, energy-dispersive spectroscopy and a serial sectioning technique to quantify porosity. The thermophysical properties were measured using differential scanning calorimetry and laser flash diffusivity testing at Thermophysical Property Measurement Laboratory, Inc. in West Lafayette, IN. The two processing routes were found to produce similar phase fractions, but resulted in different properties as a function of phase morphology and porosity content. These results suggest that future modelling and property measurement efforts must account for both the structure and composition of the slags.     

Use of farming and agro-industrial wastes as versatile barriers in reducing pesticide leaching through soil columns

Increased interest has been recently focused on assessing the influence of the addition of organic wastes related to movement of pesticides in soils of low organic matter (OM) content. This study reports the effect of two different amendments, animal manure (composted sheep manure) and agro-industrial waste (spent coffee grounds) on the mobility of 10 pesticides commonly used for pepper protection on a clay-loam soil (OM = 0.22%). The tested compounds were azoxystrobin, cyprodinil, fludioxonil, hexaconazole, kresoxim-methyl, pyrimethanil, tebuconazole, and triadimenol (fungicides), pirimicarb (insecticide), and propyzamide (herbicide). Breakthrough curves were obtained from disturbed soil columns. Cumulative curves obtained from unamended soil show a leaching of all pesticides although in different proportions (12-65% of the total mass of compound applied), showing triadimenol and pirimicarb the higher leachability. Significant correlation (r = 0.93, p<0.01) was found between the observed and bibliographical values of GUS index. The addition of the amendments used drastically reduced the movement of the studied pesticides. Only two pesticides were found in leachates from amended soils, pyrimethanil (<1%) for both, and pirimicarb (44%) in the soil amended with spent coffee grounds. A decrease in pesticide leaching was observed with the increase in dissolved organic matter (DOM) of leachates. The results obtained point to the interest in the use of organic wastes in reducing the pollution of groundwater by pesticide drainage.     

A primary study of simultaneous leaching of silver containing manganese ore and a sphalerite concentrate

It is demonstrated that a low grade, silver containing manganese deposit can be exploited by reaction with a ZnS concentrate. In the process Mn(IV) is reduced to Mn(II) and the ZnS converted to ZnSO4. In the process Mn and Zn are solubilized. By studying the effects of quantity of reducing agent and sulfuric acid added and of time, temperature and liquid-to-solid ratio on the leaching process, the optimum technological conditions have been achieved under which the amount of manganese leached was 98%. The silver can be removed from remaining solids by adding ammonia liquor. By then adding hydrazine hydrate, sponge silver with purity up to 99% can be obtained with a recovery of 87%.