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By Y. C. Liu

Ningxiang-type iron deposit is a most important sedimentary oolitic hematite deposit in China. Its? detected ore reserves are 3.72 billion tons, which is 73.5% of all detected reserves, and there are about 10 billion tons of prognostic resources. It is considered as the ?poor mine? for a long time be-cause of its difficult prooerty. But based on the ore characteristics of different deposits, the technological characteristics of ore are different with great diversity in ore baring horizon, distribution range, deposit scale, ore petrology, ore mineral assemblage and iron content. Through the study of deposit features and technological mineralogy of different Ningxiang-type of iron deposits in China, and based on industrial types and natural types of ore deposits, we divide different technological types according the technological features of the ore such as mineral composition, particle size, dissemination, occurrence of useful elements and harmful elements, the main physical and chemical properties of mineral and geological conditions of deposits, etc, moreover, propose the different utilization, mineral processing technologies and product schemes for the different types of ore.

Jan 1, 2014

This study examines the surface alteration and flotation behaviour of synthetic moncheite, PtPd(BiTe)2, in the presence of pentlandite. The telluride minerals contribute around 20% ~ 30% and up to 45% of the PGM present in the Platreef ore and are considered to be slow floating as there is evidence of these minerals reporting to the tailings. It was proposed that oxidation products from other minerals and grinding media would affect the mineral surface composition and floatability thereby causing inadvertent depression of moncheite due to precipitating ions. ToF-SIMS analyses (time of flight secondary ion mass spectrometry) was used to characterise the mineral surface as well as the extent of surface alteration. Microflotation was used to deter-mine the hydrophobicity of the synthetic minerals. Conditioning of moncheite in the presence of pentlandite reduced the flotation response of the + 38 -106µm size fraction from > 99% to 56%. This was due to pentlandite dissolution products (iron and nickel hydroxy species) which formed overlayers on the mineral surfaces thereby inhibiting the adsorption of collector. In addition, further grinding of these samples, with and without pentlandite conditioning showed a negative effect on recovery due to the fineness of the particle size distribution and there was no advantage gained from any possible exposure of fresh sites in the sample.

Jan 1, 2014

By Q. Huo

The alumina production might not continue when the sulfur content of bauxite was too high. In order to bring down the sulfur content in bauxite, we studied on the bauxite desulfurization by bacteria screened from the acid mine drainage at mines of high sulfur content. The screened bacteria were domesticated by the high sulfur content bauxite. The experiments of bauxite desulfurization were carried out under the conditions of 5% pulp density, temperature of 30?, rotate speed of 120rpm. Bacterial desulfurization for 30 days, the sulfur content of the bauxite was reduced from 5.73% to 1.55% and the desulfurization percent was 72.9%. The recovery percent of alumina was 94.3%. The study showed that it was feasible to bring down the sulfur content of bauxite by bioleaching and this technique might make full use of the low grade bauxite.

Jan 1, 2014

By Gustav Hawlitschek, Henrique Kahn, Carina Ulsen, Renato Contessotto

"The problems related to waste dumping increased with the growth and development of large cities. In the U.K., more than 50% of landfill waste comes from construction use and the U.S. alone produces around 200 to 300 million tons of CDW annually. The exhaustion of natural sand deposits close to large urban centres stimulates the recycling of construction and demolition waste for the production of recycled aggregates as a construction material. This paper presents a flowchart for the production of recycled sand with low porosity and regular shape by the selective removal of the cement paste attached to recycled aggregates. The products characterization was carried out by the determination of the particle size and shape distribution, chemical and mineralogical composition, heavy liquid mineral separation and quantification of all present phases using a scanning electron microscopy with automated image analysis (SEM-MLA). The comminution of CDW by vertical shaft impact crusher made possible the production of a lower porosity recycled sand. The heavy liquid mineral separation showed that the proportion of low porous phases (d>2.5 g/cm3) is very high, exceeding 70% of the weight, encouraging further mineral processing separation to obtain a fine recycled aggregate with less cement paste content. The mineralogical characterization by XRD and SEM indicates that the main phases are tectosilicates, phyllosilicates and calcite which one can be attributed to both calcareous aggregate and cement paste. The precise quantification of cement paste and calcite/dolomite alone is just possible by automated image analysis. The characterization results demonstrated that proportion of phases with no cement paste attached increases progressively in denser products. The results of heavy liquid separations and image analysis are comparable and automated image analysis can be used for the characterization of phase content and their main associations."

Jan 1, 2014

By G. Y. Zhou

During Zijinshan copper heap bioleaching, pyrite was leached in plenty resulting in high ferric concentration in solution. It has affected bioleaching and extraction processing greatly. It results much acid and iron in solution and bad effect to extraction processing. The paper studied the influence factors in the course of pyrite leaching and ferric ion chemical oxidation, especially studied the redox potential for copper bioleaching so as to find key factors affecting the dissolution difference between chalcocite and pyrite. The results show that the redox potential is important factor. Copper and pyrite leaching rates are 95% and 11% respectively and there is great dissolution difference between them at redox potential 700 mV (SHE). During pyrite bioleaching, the indirect action of bacteria gives priority to bioleaching cooperating with the direct attack of microbial cells attached to the mineral surface. Redox potential is determined by ratio of ferric and ferrous, ferric in solution was supplied by the way of oxidation of T. f bacteria, sufficient bacteria concentration and active character were two vial factors of controlling redox potential. It is indicated that copper can be selectively bioleached during copper bioleaching by controlling redox potential of bioleaching. The conclusion will provide theoretic foundation on balance of acid and iron during bioleaching for copper of higher S/Cu ratio. The experinment proved that bacteria activation was decreased on condition of both low pH value and intermittent aeratation during bioleaching. It resulted that the oxidation velocity of ferrous ion was decreased and redox potential was controlled. The dissolution of pyrite was depressed. It would be possible to actualize selective leaching of secondary sulfide copper ore during bioleaching process.

Jan 1, 2014

By William Conger, Greg Schick

Grinding media consumption is a major cost variable in industrial mineral comminution circuits. Specifically, industrial SAG media consumption results from a combination of surface abrasion wear, media breakage, surface spalling and rejection size from the mill. Three main consumption rates; weight of media consumed per time, per kWh and per weight of ore ground are defined and compared. Recent industrial data has provided an opportunity to relate consumption in terms of weight of media consumed to weight of ore ground (g/tonne) and weight of media consumed per kWh of energy consumed (g/kWh) with SAG specific grinding energy consumed (kWh/tonne). Using relationships developed from this data it is possible to project SAG media consumption in future mineral comminution circuits.

Jan 1, 2014

By S. Fiore, M. C. Zanetti, C. Clerici

The processes and fluxes of a cast iron foundry plant located in the North of Italy were analyzed in order to determine the amount and kind of wastes produced from the different activities. The main fractions are the molding sands, furnace muds and powders coming from the dust abatement plant, the exhaust lime, the furnace refractory, the metallic shotting and the sludges and powders coming from the dust abatement plant of molding lines for a total production equal to 800 t/d. All wastes were sampled and particle-size and chemically characterized to evaluate the best recycling or reuse solutions. Wastes were sieved and divided in three categories according to the particle-size dimensions: below 0.1 mm, between 0.1 and 0.6 mm and above 0.6 mm. The fraction above 0.6 mm dimension underwent magnetic separation to recover and quantify the potentially available iron fraction. The fraction between 0.1 mm and 0.6 mm was chemically characterized in order to understand if it could be fed to the sand regeneration plant. The below 0.1 mm fraction was characterized to evaluate the following recycling and reuse solutions: additive for molding sands and/or raw material for the concrete industry.

Jan 1, 2003

At times the phosphate industry, in Florida, encounters phosphate rock that gives lower than expected P2O5 recovery in the rougher plant section. The drop in recovery is typically 10% and as much as 30% or more. Variations in feed quality from day to day, shift to shift and even from drag-line to drag line, represent a challenge to the beneficiation plant operators and reagents? suppliers. Therefore, this characterization study has been initiated to identify the reasons for the differences in flotation behavior of such feeds. The study involves many samples to cover such variations. The characterization work includes: ? Mineralogical and chemical analysis; ? Size, shape, surface roughness and porosity analysis; ? Surface charge and surface contamination with other phases (minerals); ? Clay content and its relationship to phosphate and silica particles. The results correlated with flotation data and adsorption density measurements clearly establish the statistically significant variability in characteristic features that influence flotation response. This article discusses results from the above listed studies. On the basis of the obtained data, recommendations of practical approaches to overcome the problem of feed variability in phosphate flotation plants are delineated.

Jan 1, 2014

By Yang Zhao, Tao Xiu-xiang, Chen Song-jiang

"China is rich in low-rank coals that account for 45.68% of existing coal reserves in China. The clean and efficient utilization of low rank coals is of great significance for ensuring the effective energy supply and promoting economic development and environmental protection. In order to solve the difficult problem in flotation of low rank coal, it has become the focus of research in the related field that oily bubbles instead of air bubbles are taken as a carrier in flotation to improve the attachment efficiency and recovery of low rank coal. In this paper, low rank coal slime collected from Shendong mining area was used as the experimental material, and it focused on the characteristics of oily-bubble flotation process of low rank coal. Additionally, difference in conventional flotation and oily-bubble flotation was discussed. The induction time between air bubbles, oily-bubbles and fine low rank coal particles was measured. The results indicated that the induction time between oily-bubbles and coal particles was obviously lower than that of air bubbles. By comparing the foam height of air and oily bubbles, it was found that the amount of oily bubbles is less than air bubbles, causing relative low flotation rate of oily-bubble flotation at initial stage. Besides, the maximum foam height and half-life of air bubbles and oily-bubbles were measured respectively. The results showed that the stability of oily-bubbles was higher than that of air bubbles, which is benefit for the enrichment of concentrates. The clean coal water recovery of oily-bubble flotation is lower than that of air bubble flotation, which indicated oily-bubble flotation is lower in water entrainment. INTRODUCTION China is the largest energy consumer in the world, accounting for 23% of global energy consumption in 2016 and 27% of global energy consumption growth. Whereas coal is taken as the major primary energy source and its share of China’s primary energy consumption is 62% in 2016, in which the low rank coals, such as lignite, long-flame coal, weakly caking coal, and non-caking coal, accounted for about 50% of total coal production capacity (China’s energy market in 2016, BP). Moreover, the exploitation and utilization of low rank coals and other coals that are difficult to float have been an important strategy for China’s sustainable development of the coal industry (Liu et al., 2014). However, the combustion of low-quality coals leads to a serious environmental pollution. In addition, the deterioration in geological conditions of coal resources, and the increasing improvement in the mechanization for mining significantly caused the increased amount of fine coal."

Jan 1, 2018

By Wenqing Qin, Yunfan Wang, Ximei Luo, Fen Jiao

In order to investigate the effect of nanobubbles on adsorption of surfactant on mineral surface, the nanobubbles on the surface of calcite with -37µm fraction in the sodium oleate system were controlled by pressurization and decompression to mixing vessel. Subsequently, the adsorption amount of sodium oleate on the surface of calcite were detected by ultraviolet spectrum at different stirring times and different pressures. At the same time, the nanobubbles on the calcite surface were imaged with atomic force microscopy (AFM). In addition, a homemade vacuum Hallimond tube device was used for the flotation of single mineral, and the grade and recovery of minerals in concentrate was used to determine the influence of the nanobubbles on flotation. The experimental results showed that a large number of nanobubbles were found on the calcite surface by AFM under the dissolved oxygen difference (DOD) condition of -4 mg/L. And a large difference in adsorption capacity of sodium oleate on the surface of calcite was observed under different air pressure conditions. It indicated that the ambient pressure had a certain effect on the adsorption of sodium oleate on the calcite surface, and this effect did not depend on the constant low pressure or constant normal pressure, but depended on the changing process of pressure. The single mineral flotation experiment results indicated the recovery of calcite under decompression condition (formation condition of nanobubbles) was 1.5-2 times that under constant normal pressure, and the flotation time is much shorter. Moreover, the recovery under constant normal pressure was greatly influenced by flotation time. In this paper, only one aspect of the effect of nanobubbles on mineral flotation was preliminarily explored. It was confirmed that after vacuum-pumping, the adsorption of sodium oleate on calcite surface could be increased, the flotation time also was greatly reduced and the recovery of calcite was increased.

Jan 1, 2018

By Graeme Lane, Yuqing Feng, Kaixi Jiang, Junwu Zhou, Zhengchang Shen, Tao Song

"Airlift reactors are used in a wide range of industries, such as hydrometallurgy, biochemical processes, chemical process industry and waste water treatment. With increasing superficial gas velocity three circulation regimes can be defined: no gas bubbles in the downcomer, gas bubbles remain stationary in the downcomer and gas bubbles in the circulating regime. In this paper a numerical modelling method was presented for gas-liquid flow in airlift reactors under different bubble recirculation regimes. Gas-liquid flow was modelled using the Eulerian two-fluid equations, and extra user defined subroutines were incorporated to consider the complex physics, such as bubble induced turbulence and turbulent dispersion force. Some alternative correlations of drag coefficient were used to capture the bubble distributions in the riser and downcomer of the airlift reactor, with consideration of the interaction between bubbles. As using constant bubble size is hard to describe global characteristics of the flow in airlift reactors for three circulation regimes, a model including multiple bubble sizes was presented to get more accurate simulation results of gas holdup and water velocity. Also, the inhomogeneous MUSIG model was used, as an exploration, to compute the complex flow regimes. The MUSIG model is a population balance method to predict the bubble sizes, taking break-up and coalescence into account. The modelling method was applied to a laboratory internal loop airlift reactor, and the simulation results were compared with the experimental measurements of Simcik et al. (2011) for gas holdup and water velocity. The three bubble circulation regimes were observed from simulation figures. Reasonable agreement was obtained over a range of operating conditions, and an improvement was demonstrated using the proposed methods."

Jan 1, 2014

By Christian O’Keefe, Alex Van der Spek

"Evaluation of inequalities of the partial sums defining cumulative grade and recovery prove that cumulative grade has an upper bound not dependent on the bank number and cumulative recovery possesses an upper bound proportional to the bank number. This explains one observed characteristic of cumulative grade versus cumulative recovery curves. The existence of such maxima combined with the observed shape of cumulative grade-recovery curves leads us to postulate that these curves can be well described by rectangular hyperbolae. Rectangular hyperbolae are characterized by asymptotes at right angles to each other. It is proven that this property can be used to derive an equation for the cumulative mass flow of the concentrate in terms of the asymptotic values of cumulative grade and cumulative recovery. Fitting hyperbolae to experimental cumulative grade cumulative recovery plant data then results in estimates of the maximum grade, the maximum recovery and a constant which may be taken as a performance coefficient of a row. Normalization of the cumulative grade and the cumulative recovery by their respective maxima gives rise to a graphical representation that can be used to evaluate the operating performance of a row of floatation bank cells. The normalization procedure removes the bias that is introduced by inevitable variation in mass flow of the feed and variation in feed mineralogy or feed particle size distribution. Reduction of the normalized data collapses all cumulative grade-recovery data onto one and the same curve. This removes the differences caused by the variation in row performance. The reduced cumulative grade-recovery data scatters around a common hyperbola. This can be used to gauge the validity of the assumptions made. Normalized cumulative mass pull is determined from the fitted values of the maximum recovery and maximum grade. This may serve as an alternative performance indicator of the floatation row."

Jan 1, 2014

By Joseph Kelly, Christopher Kelsey

This revolutionary super-fine crusher has the unique capacity to generate fine and ultra-fine products from single stage reductions of coarse or fine mineral feeds. The crusher consists of a rotating compression chamber and an internal gyrating mandrel. The axis of rotation of the shell is displaced relative to the axis of the vertically mounted mandrel. The inner surface of the compression chamber is machined as double cone frustums at an angle equal to the displacement angle. Crusher feed is accelerated into a compacted particle bed, which lines the inside of the compression chamber. The depth of the compacted bed progressively increases until the mandrel is engaged. The mandrel is then free to rotate with the compression chamber. Continued feeding increases power draw and triggers the counter rotating mandrel gyration drive. The gyrating mandrel delivers multiple compressions at high pressure to the rotating particle bed. High concentrations of energy are harnessed within a small active volume over short retention times. The combination of extraordinarily high power intensity and extreme compressive force results in primary compressive fracture and induced secondary tensile failure. The axially displaced rotation of the compression chamber effectively distributes the breakage forces throughout the particle bed. This paper covers open circuit, pilot trials on magnetite, perlite, garnet, marble and a copper/pyrite concentrate. Particular emphasis is placed on the extraordinary results achieved with trials on zircon and highly refractory fly ash. The extreme duties were deliberately chosen to demonstrate the crusher’s application scope and potential to impact capital operating and maintenance costs as the technology matures. Super-fine crushing, once considered impracticable has the potential to offer compelling options for the generation of ultra-fine products.

Jan 1, 2014

By X. F. Cao

There was a large reserve of bauxite resources in China. And these resources were mainly the dias-pore-bauxite and contained plenty of aluminosilicate including kaolinite, illite and pyrophyllite. Reducing the contents of aluminosilicate would be significant to the using of Chinese bauxite resources. In this paper, from the single mineral flotation experiments, the surface properties and flotation beha-viours of aluminosilicate including kaolinite, illite and pyrophyllite, using dodecyl amine (DDA), N, N-dimethyl-dodecyl amine (DRN12) and N-dodecyl-1, 3-propane diamine (DN12) as collectors, had been investigated. The flotation results shown that the flotation behaviours of aluminosilicate had been influenced greatly by three amine collectors; and the effect was in the order of DN12>DRN12 >DDA. On the basis of FT-IR spectra and zeta potential measurements, the ionization of surface hydroxyl, as well as isomorphic exchange of surface ions, accounted for the mineral surface charges. And the mechanisms of interactions between the mineral surface and collectors mainly included two modes: electrostatic adsorption and hydrogen bonding; for the DDA and DRN>DDA. 12, the mechanism was mainly electrostatic adsorption; and for the DN12, the mechanisms of electrostatic adsorption and hydrogen bonding both existed. Results of quantum chemistry research shown that the collecting ability of amine collectors was greatly influenced by the electro-negativity of N in the amine molecules; and The |E(EHOMO| and ?E (HOMO-ELUMO) of N atom in DRN12 and DN12 were lower than that of DDA, and the positive charge of ?N group in DRN12 and DA12 were higher than that of DDA. All these calculation results could explain the collecting power of DN12>DRN12>DDA.

Jan 1, 2014

By A. Prokopiev

The biological stage of reclamation is the third final stage in remediation the damaged mining terrains, which is carried out following the completion of the mining technical stage. The biological stage of reclamation is carried out through restoration of the vegetation layer. The biological reclamation includes all activities related to the introduction into the terrain of vegetation, microorganisms, insects, and animals, with the acceleration of the succession and creating conditions for a sustainable ecosystem close to the natural one. It comprises of all anti erosion and other activities such as the preparation of the land for growing agricultural crops, sowing grass seeds, planting seedlings, amelioration of the soil and further care for the vegetation until its final place on the land. Mineral and organic-mineral ameliorants for biological reclamation were studied. The basic mineral ameliorant is Bulgarian natural zeolites. The zeolitic-rich tuff samples provided from Golobradovo deposit was characterized by their chemical and mineralogical composition and ion exchange properties and X ray analysis. The average content of clinoptilolite was found to be more than 80%. The materials had ion exchange capacity (NH4+) varying from 100 to 110 meq/100g. Chemical modifications of natural clinoptilolites were made in order to form active phases of nitrogen, phosphorus, potassium, and microelements. Slow-acting mineral ameliorant was developed. Organic-zeolite substrate for biological reclamation was developed. This new product is a mechanical mixture of organo-matter and modified zeolites. Agro-chemical parameters of new ameliorants were determined. The substrates including studied overburden dump soil and mineral or organo-mineral ameliorants are produced. The grass growth test was performed. Keywords: biological reclamation, ameliorants, damaged mining terrains

Sep 1, 2012

By J. Temuujin

Mongolia has some of the world?s largest coal reserves with an estimated total coal reserve of over 150 billion tonnes. At present, over 90% of Mongolian electricity is produced by combined heat and thermal power stations. The main coal deposits used for Central power system's power stations are Baganuur, Shivee-ovoo lignite type coal and Shariin gol bituminous coal. In Mongolia almost 600,000 tonnes of coal combustion by-products are disposed of in waste ponds. In this research, we have thoroughly characterized Mongolian coal combustion by-products including fly ashes sourced directly from thermal power stations and ash retrieved from ponds. It was determined that fly ashes generated from Baganuur and Shivee-ovoo coal deposits are class C, while ash from Shariin gol coal is class F (according the ASTM C618). All ash products were characterized by chemical, mineralogical, granulometrical, porosity, FE-SEM and radiation methods. Fly ashes sourced directly from power stations were found to be more suitable for manufacture of geopolymers for building materials application and zeolite synthesis than ashes retrieved from ash ponds. The adsorption and porous properties of zeolitic compounds were measured and found to be suitable for adsorption of Cr6+ from simulated tannery waste water. Keywords: coal, coal combustion by products, synthesis, geopolymers, zeolitic compound

Sep 1, 2012

By Jacob Masliyah, Zhenghe Xu, Lujie Yan

"Understanding adsorption mechanism of polymeric organic process modifierssuch as carboxymethyl cellulose (CMC) on talc hasbeen a major challenge due to anisotropic nature of talc basal planes and edge surfaces. The main objective of this study is to investigate the adsorption of CMC on the basal planes and edge surfaces of talc.Smooth basal plane and edge surfaces of talc were prepared successfully by simple cleavage and sophisticated ultramicrotome cutting method, respectively. The prepared surfaces were characterized by atomic force microscope (AFM) imaging to be sufficiently smooth for colloidal probe force measurements using AFM. Anisotropic surface charge characteristics were determined,with the basal planes to carry a permanent negative surface charge and edge surfaces featuring a pH-dependent charge characteristic. The adsorption of CMC on talc basal plane and edge surfaces at pH 9 in KClaqueous solutions of various ionic strengths wasinvestigated by in situ AFM imaging technique. Themorphology of adsorbed CMC on talc basal planes and edge surfaces was found to be significantly different, due to different binding mechanisms involved. Interaction of CMC with the talc basal plane was found to bedominated by hydrophobic interactions while its binding with the talc edge surface was mainly through chemical complexation and hydrogen bond. The amount of CMC adsorbed on both talc basal planes and edge surfaces increased with increasing ionic strengthof solutions. The methodology developed in our study opens the door to probe polymer adsorption on anisotropic phyllosilicate surfaces, which can help us better understand the mechanism of polymer adsorption on specific mineral faces."

Jan 1, 2014

By R. Singh

The paper presents the results of characterization and beneficiation studies carried out on a lean grade tungsten ore sample from Degana, India. Basically, three different routes, involving gravity separation, magnetic separation, and froth flotation were studied for concentration of the sample by physical and physico-chemical methods. Considering the low recovery by physical methods, efforts were put in to produce a tungsten concentrate by physical methods suitable for subsequent hydrometallurgical recovery of tungsten as ammonium para-tungstate. This strategy proved quite helpful in minimizing the losses of tungsten in tailings. Based upon these studies a novel integrated technological process flow-sheet was developed for the exploitation of lean grade tungsten ore deposit of Degana, India. Keywords: lean tungsten ore, characterization, beneficiation, gravity and magnetic separation, hydrometallurgical extraction, integrated process route

Sep 1, 2012

By Carlos Collado, Oscar Jimenez, Francisco Diaz, Rodrigo Bernal, Carmen Salinas

Water is a strategic resource for the mining industry. The rising cost has forced the industry to become more efficient in their use, reduce and recycle waste as much as possible. The importance of having a reliable water balance is increasingly urgent, because the resource is scarce and vital to the sustainability of human life, animal and ecosystem. Conventional flowmeters can suffer disruptions or failures by corrosion, fouling, presence of elements in the water as acids, salts and suspended solids. Use of radiotracers is advantageous to determine fluid velocities that are transported through pipes, as they are detectable by means of the radiation emitted, the same way for surface flows, such as natural watercourses and drainage from tailings dams, fluorescent tracers are those with the best advantages. For velocity measurements in pipelines a Iodine-131 tracer solution, around 5 mCi was injected into the suction of the pumps. The technique used is the transit time between detectors at known distances and determining the time of passage of the radiotracer. For measurements of surface fluxes using the fluorescent tracer Rhodamine WT by tracer dilution technique, injecting the tracer at a constant rate and measuring it known concentration diluted downstream. This work has been performed in Minera Los Pelambres, located in the IV Region of Chile, measuring the flow rate pumped from 12 pools with 1-7 pumps operating, obtaining speeds of 0.56 to 2.62 m/s. In pumping wells three facilities have been measured at speeds of 0.111-0.223 m/s, plus six surface flows with flow rates of 8.45 to 357.2 L/s.

Jan 1, 2014

By C. Stollberg

The recovery of valuable materials from electronic waste is of growing importance for the re-source management not only in the industrialized nations. Being a significant step in an innovative automated process for recycling of metals and plastics from used electric and electronic equipment, the results of the work introduced below, prove the applicability of microbial leaching of metals from printed circuit boards (PCBs) at industrial scale. Within the first project step, which started in March 2005, experiments in shaking flasks with a mixed culture of chemolitotrophic bacteria (mainly Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans) were carried out to study the solubilization of non-ferrous metals present in the electronic waste. It was found that the best results were achieved by means of a two-stage process in which leaching of these metals was carried out by acidified ferric sulphate solutions generated as a result of the prior bacterial oxidation of ferrous ions to the ferric state. Special reactor systems for bacterial generation of such solutions and for the subsequent leaching of non-ferrous metals from the waste were developed, constructed and tested under laboratory and pilot scale conditions. The optimum technological parameters such as concentration of iron ions, pH-value, temperature and presence of nutrients were established for both reactor systems. Parameters such as particle size, pulp density and flow rate of the suspensions being leached were established for the leaching process carried out under continuous-flow conditions. The complex flow sheet reflects a highly efficient technology on the basis of metal recovery, environmental effect and economical acceptance. The process was successfully implemented into an industrial demonstration unit.

Jan 1, 2014