Recent trends and current practices for secondary processing of zinc and lead. Part II: zinc recovery from secondary sources.

Almost all metallurgical processes are associated with the generation of wastes and residues that may be hazardous or non-hazardous in nature depending upon the criteria specified by institutions such as the US Environment Protection Agency, etc. Wastes containing heavy and toxic metals such as arsenic, cadmium, chromium, nickel, lead, copper, mercury, zinc, etc., that are present beyond permissible limits deemed to be treated or disposed of, and non-hazardous wastes can be utilized for metal recovery or safe disposal. Zinc is in growing demand all over the world. In India, a major amount of zinc is imported and therefore processing of zinc secondaries will assist in satisfying the gap between demand and supply to some extent. This report mainly focuses on the current practices and recent trends on the secondary processing of zinc. Attempts made by various laboratories to develop ecofriendly processes for the recovery of zinc from secondary raw materials are also described and discussed.     

Bio-processing of solid wastes and secondary resources for metal extraction - A review

Metal containing wastes/byproducts of various industries, used consumer goods, and municipal waste are potential pollutants, if not treated properly. They may also be important secondary resources if processed in eco-friendly manner for secured supply of contained metals/materials. Bio-extraction of metals from such resources with microbes such as bacteria, fungi and archaea is being increasingly explored to meet the twin objectives of resource recycling and pollution mitigation. This review focuses on the bio-processing of solid wastes/byproducts of metallurgical and manufacturing industries, chemical/petrochemical plants, electroplating and tanning units, besides sewage sludge and fly ash of municipal incinerators, electronic wastes (e-wastes/PCBs), used batteries, etc. An assessment has been made to quantify the wastes generated and its compositions, microbes used, metal leaching efficiency etc. Processing of certain effluents and wastewaters comprising of metals is also included in brief. Future directions of research are highlighted.     

An overview of recovery of metals from slags

Various slags are produced as by-products in metallurgical processes or as residues in incineration processes. According to the origins and the characteristics, the main slags can be classified into three categories, namely ferrous slag, non-ferrous slag and incineration slag. This paper analysed and summarised the generation, characteristics and application of various slags, and discussed the potential effects of the slags on the environment. On this basis, a review of a number of methods for recovery of metals from the slags was made. It can be seen that a large amount of slags is produced each year. They usually contain a quantity of valuable metals except for blast furnace slag and they are actually a secondary resource of metals. By applying mineral processing technologies, such as crushing, grinding, magnetic separation, eddy current separation, flotation and so on, leaching or roasting, it is possible to recover metals such as Fe, Cr, Cu, Al, Pb, Zn, Co, Ni, Nb, Ta, Au, and Ag etc. from the slags. Recovery of metals from the slags and utilisation of the slags are important not only for saving metal resources, but also for protecting the environment.     

An overview of metals recovery from thermal power plant solid wastes

Thermal power plants (TPPs) that burn fossil fuels emit several pollutants linked to the environmental problems of acid rain, urban ozone, and the possibility of global climate change. As coal is burned in a power plant, its noncombustible mineral content is partitioned into bottom ash, which remains in the furnace, and fly ash, which rises with flue gases. Two other by-products of coal combustion air-pollution control technologies are flue gas desulfurization (FGD) wastes and fluidized-bed combustion (FBC) wastes. This paper analyzed and summarized the generation, characteristics and application of TPP solid wastes and discussed the potential effects of such solid wastes on the environment. On this basis, a review of a number of methods for recovery of metals from TPP solid wastes was made. They usually contain a quantity of valuable metals and they are actually a secondary resource of metals. By applying mineral processing technologies and hydrometallurgical and biohydrometallurgical processes, it is possible to recover metals such as Al, Ga, Ge, Ca, Cd, Fe, Hg, Mg, Na, Ni, Pb, Ra, Th, V, Zn, etc., from TPP solid wastes. Recovery of metals from such wastes and its utilization are important not only for saving metal resources, but also for protecting the environment.     

Electrostatic separators of particles: Application to plastic/metal, metal/metal and plastic/plastic mixtures

Electrostatic separation is a generic term given to a significant class of technologies of industrial waste processing, widely used for the sorting of granular mixtures due to electric forces acting on particles whose average size is approximately 5mm. The focus of this paper is on three electrostatic processes of separation used for processing of different types of mixtures: (i) role-type electrostatic separator, used to sort mixtures containing metal/plastic particles (copper/PVC for example); (ii) plate-type electrostatic separator, used to sort mixtures containing metal/metal particles (copper/lead for example) and (iii) free-fall electrostatic separator, used to sort mixtures of plastic/plastic particles (PVC/PE for example). Experiments carried out on industrial samples using laboratory electrostatic separators confirm the efficiency of these processes and show that the processes can improve the recovery and purity of products resulting from industrial wastes.     

Accelerated carbonation treatment of industrial wastes

The disposal of industrial waste presents major logistical, financial and environmental issues. Technologies that can reduce the hazardous properties of wastes are urgently required. In the present work, a number of industrial wastes arising from the cement, metallurgical, paper, waste disposal and energy industries were treated with accelerated carbonation. In this process carbonation was effected by exposing the waste to pure carbon dioxide gas. The paper and cement wastes chemically combined with up to 25% by weight of gas. The reactivity of the wastes to carbon dioxide was controlled by their constituent minerals, and not by their elemental composition, as previously postulated. Similarly, microstructural alteration upon carbonation was primarily influenced by mineralogy. Many of the thermal wastes tested were classified as hazardous, based upon regulated metal content and pH. Treatment by accelerated carbonation reduced the leaching of certain metals, aiding the disposal of many as stable non-reactive wastes. Significant volumes of carbon dioxide were sequestrated into the accelerated carbonated treated wastes.     

Thermal treatment and decontamination of mercury-contaminated waste: Recent developments and comparative evaluation

The land disposal restriction regulations have necessitated development of technologies for the treatment of wastes and soils containing mercury. Of all the treatment methods, thermal technologies are the most advanced and proven for a variety of mercury-contaminated waste materials. During the past few years, a number of thermal treatment processes have been developed both for listed and characteristic waste. A review of the technologies identified six that are in either commercial or pilot plant stages. The biggest volumes of waste currently occur in the gas processing and caustic-chlorine industries, so most of the technologies being used appear to have been developed around the characteristics of these two wastes. This article discusses the characteristics of each of the six available thermal treatment processes, and describes the types of mercury-contaminated wastes these technologies have been designed to handle.     

Bioleaching of metals from spent lithium ion secondary batteries using Acidithiobacillus ferrooxidans

Bioleaching of spent lithium ion secondary batteries, containing LiCoO2, was attempted in this investigation. The present study was carried out using chemolithotrophic and acidophilic bacteria Acidithiobacillus ferrooxidans, which utilized elemental sulfur and ferrous ion as the energy source to produce metabolites like sulfuric acids and ferric ion in the leaching medium. These metabolites helped dissolve metals from spent batteries. Bio-dissolution of cobalt was found to be faster than lithium. The effect of initial Fe(II) concentration, initial pH and solid/liquid (w/v) ratio during bioleaching of spent battery wastes were studied in detail. Higher Fe(II) concentration showed a decrease in dissolution due co-precipitation of Fe(III) with the metals in the residues. The higher solid/liquid ratio (w/v) also affected the metal dissolution by arresting the cell growth due to increased metal concentration in the waste sample. An EDXA mapping was carried out to compare the solubility of both cobalt and lithium, and the slow dissolution rate was clearly found from the figures.     

Sustainable Bio-Composites from Renewable Resources: Opportunities and Challenges in the Green Materials World

Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.     

Framework for estimating potential wastes and secondary resources accumulated within an economy – A case study of construction minerals in Japan

Material stocks in economic society are considered to represent a reserve for wastes and secondary resources. From the viewpoints of proper disposal and reutilization of stocked materials, accurate estimation of the amount of materials that will emerge as wastes or secondary resources in the future is important. We defined materials that have a high probability of emerging as wastes or secondary resources as “potential wastes and secondary resources” and estimated that amount for construction minerals in Japan as a case study. The following conclusions were drawn. (1) We classified materials that are input into economic society into four categories: potential wastes and secondary resources, potential dissipated materials, dissipatively used materials, and permanent structures. By clarifying the latter three non-potential wastes and secondary resources, we performed a more accurate assessment of the wastes and secondary resources that will emerge in the future. (2) The share of potential wastes and secondary resources was estimated to be about 30% of all construction minerals that have been input into and accumulated in Japanese economic society. (3) Information related to potential dissipated materials and dissipatively used materials will provide fundamental knowledge to support analyses of the environmental impacts and resource losses which these materials might generate.     

Metallic-phase lead in slag of municipal solid waste incineration ash and leaching characteristics

Metallic phases in slags and their influence on the leaching characteristics were investigated. The proportions of metallic phase in four slags were 0.028%, 0.24%, 1.87%, and 3.05% by weight. The lead content was 10–248 mg/kg in bulk slag after metal removal, while in the metallic phase it was 579–7390 mg/kg. Lead concentrations in the metallic phase were more than ten times higher than in slags after metal removal. Lead was distributed in the metallic phase at 2.0%, 8.3%, 10.3%, and 47.4%. The concentrations of all metallic elements in metallic phases were much higher than in bulk slag. Iron, copper, and nickel had accumulated in magnetic metals, while aluminum and zinc were found in nonmagnetic metals. As regards chromium, manganese, lead, and tin, the proportion of metallic phases depended on the slag samples. By removing metallic phases, both water and pH 4 leachable lead decreased. The basic principles of melting residues containing lead are the separation of lead as a metal in reductive melting, and the containment of lead ions into uniform glassy particles in oxidization melting. Melting slag can be seen to contribute to environmental preservation by facilitating the recycling of materials through the separation of metals from melting slag. Received: February 21, 2000 / Accepted: July 27, 2000     

Characterization of residues from dismantled imported wastes

Residues from the imported wastes dismantling process create a great burden on the ambient environment. To develop appropriate strategies for the disposal of such residues, their characteristics were studied through background value analysis and toxicity leaching tests. Our results showed that the heavy metals concentrations in residues were high, particularly those of Cu (7180 mg kg^?1), Zn (2783 mg kg^?1), and Pb (1954 mg kg^?1). Toxicity leaching tests revealed a high metal releasing risk of such residues if they are disposed of in a landfill. However, the residues of imported wastes were also found to have some intrinsic metal recycling value.     

Biodegradation and flushing of MBT wastes

Mechanical–biological treatment (MBT) processes are increasingly being adopted as a means of diverting biodegradable municipal waste (BMW) from landfill, for example to comply with the EU Landfill Directive. However, there is considerable uncertainty concerning the residual pollution potential of such wastes. This paper presents the results of laboratory experiments on two different MBT waste residues, carried out to investigate the remaining potential for the generation of greenhouse gases and the flushing of contaminants from these materials when landfilled. The potential for gas generation was found to be between 8% and 20% of that for raw MSW. Pretreatment of the waste reduced the potential for the release of organic carbon, ammoniacal nitrogen, and heavy metal contents into the leachate; and reduced the residual carbon remaining in the waste after final degradation from ～320 g/kg dry matter for raw MSW to between 183 and 195 g/kg dry matter for the MBT wastes.     

Cement clinker: An environmental sink for residues from hazardous waste treatment in cement kilns

About 70% of all of the liquid and solid hazardous wastes commercially incinerated in the United States is being burned in cement kilns. The process inevitably results in residues, primarily heavy metals, entering the clinker and waste dusts (cement kiln dust, CKD) produced by these kilns. The effects of this trend on the nature and chemical composition of cement, actual and future, are discussed. The wastes burned by cement kilns are expected to increasingly have higher levels of heavy metals per Btu. In general, the effects are very simple to describe but have as yet unknown consequences. The present American Society for Testing and Materials (ASTM) standard does not effectively control hazardous waste burning residues in Portland Cement.The regulatory and economic pressures on CKD disposal suggest that much of it, and its heavy metal residues, will, in time, end up in the clinker and the resultant cement. The end point to the trend is the ability to make cement that passes the performance specifications while containing high levels of heavy metals. The only other alternative is to maximize the levels of heavy metals in the CKD, minimize the amount of CKD, and dispose of its as a hazardous waste.It is recommended that an effort to correlate heavy metal levels in clinker with adverse effects be undertaken, a new standard for cement containing hazardous and other waste residuals be developed, and labeling be required.     

Agrochemical characterisation of the solid by-products and residues from the winery and distillery industry

The winery and distillery industry produces a great quantity of residues, whose management and disposal are environmental problems due to their seasonal character and some polluting characteristics. The main solid by-products and residues generated are grape stalk, grape pomace or marc, wine lee, exhausted grape marc and winery sludge. In this study, 87 samples of winery and distillery residues were collected from different Spanish wineries and distilleries. Electrical conductivity, pH, total organic matter, organic carbon, polyphenols and contents of plant nutrients and heavy metals were determined. The purpose of this research was to study the composition of these wastes and to find relationships in order to use easily analysable parameters to estimate their composition. In general, the winery and distillery residues showed low pH (mean values ranged from 3.8 to 6.8) and electrical conductivity values (1.62-6.15 dS m(-1)) and high organic matter (669-920 g kg(-1)) and macronutrient contents, especially in K (11.9-72.8 g kg(-1)). However, a notable polyphenol concentration (1.2-19.0 g kg(-1)) and low micronutrient and heavy metal contents were also observed, some of these properties being incompatible with agricultural requirements. Therefore, conditioning treatments are necessary prior to possible use of these wastes. In all wastes, significant correlations were found between easily determined parameters, such as pH, electrical conductivity and total organic matter, and most of the parameters studied. The regression models obtained are also discussed.     

Beyond the material grave: Life Cycle Impact Assessment of leaching from secondary materials in road and earth constructions

In industrialized countries, large amounts of mineral wastes are produced. They are re-used in various ways, particularly in road and earth constructions, substituting primary resources such as gravel. However, they may also contain pollutants, such as heavy metals, which may be leached to the groundwater. The toxic impacts of these emissions are so far often neglected within Life Cycle Assessments (LCA) of products or waste treatment services and thus, potentially large environmental impacts are currently missed. This study aims at closing this gap by assessing the ecotoxic impacts of heavy metal leaching from industrial mineral wastes in road and earth constructions. The flows of metals such as Sb, As, Pb, Cd, Cr, Cu, Mo, Ni, V and Zn originating from three typical constructions to the environment are quantified, their fate in the environment is assessed and potential ecotoxic effects evaluated. For our reference country, Germany, the industrial wastes that are applied as Granular Secondary Construction Material (GSCM) carry more than 45,000 t of diverse heavy metals per year. Depending on the material quality and construction type applied, up to 150 t of heavy metals may leach to the environment within the first 100 years after construction. Heavy metal retardation in subsoil can potentially reduce the fate to groundwater by up to 100%. One major challenge of integrating leaching from constructions into macro-scale LCA frameworks is the high variability in micro-scale technical and geographical factors, such as material qualities, construction types and soil types. In our work, we consider a broad range of parameter values in the modeling of leaching and fate. This allows distinguishing between the impacts of various road constructions, as well as sites with different soil properties. The findings of this study promote the quantitative consideration of environmental impacts of long-term leaching in Life Cycle Assessment, complementing site-specific risk assessment, for the design of waste management strategies, particularly in the construction sector.     

Environmentally sustainable applications of agro-based spent mushroom substrate (SMS): an overview

Agricultural wastes such as lignocellulosic residues are renewable resources can be used for mushroom cultivation. Spent mushroom substrate (SMS) is defined as leftover of biomass generated by commercial mushroom industries after harvesting period of mushroom. Mushroom cultivation using agricultural wastes promises a good quality of SMS for producing beneficial products such as animal feeding and fertilizers. Based on the published papers, the major applications of SMS are animal feedstock, fertilizer, energy production and wastewater treatment. For instance, some species of mushroom such as Pleurotus spp. and Agaricus bisporus are suitable for applications of ruminant feedstock and fertilizers. This paper reviews the recent studies about the beneficial usage of SMS which is considered as a waste since 2013.     

Air pollution control residues from waste incineration: current UK situation and assessment of alternative technologies

Current disposal options for APC residues in the UK and alternative treatment technologies developed world-wide have been reviewed. APC residues are currently landfilled in the UK where they undergo in situ solidification, although the future acceptability of this option is uncertain because the EU waste acceptance criteria (WAC) introduce strict limits on leaching that are difficult to achieve. Other APC residue treatment processes have been developed which are reported to reduce leaching to below relevant regulatory limits. The Ferrox process, the VKI process, the WES-PHix process, stabilisation/solidification using cementitious binders and a range of thermal treatment processes are reviewed. Thermal treatment technologies convert APC residues combined with other wastes into inert glass or glass-ceramics that encapsulate heavy metals. The waste management industry will inevitably use the cheapest available option for treating APC residues and strict interpretation and enforcement of waste legislation is required if new, potentially more sustainable technologies are to become commercially viable.     

Utilization of post-production waste from fruit processing for energetic purposes: analysis of Polish potential and case study

There is no doubt that waste products from fruit and vegetable processing are difficult to manage. In that context, partial substitution of conventional energy substrates by industrial waste is an alternative, as it helps to utilize residues and at the same time to reduce the fixed cost of running business. The aim of the article is to analyse the possibilities of using fruit processing wastes for energy purposes in Poland. The assessment on a country scale was based on the data of the Central Statistical Office. Analogical analysis was based on the data collected from selected production plant. The obtained results show that the fruit processing waste can be successfully utilized for energy purposes. At the same time, problems of organizational nature should not be overlooked, as they can significantly decrease that potential. Although the amount of energy obtained from this source is basically negligible in the Polish energy balance, the environmental factor should not be ignored also. Therefore, the utilization of waste products from fruit processing should be a topic of interest, as it works in two ways, i.e., through reducing the amount of waste and increasing production of renewable energy.

     

Valorization of titanium metal wastes as tanning agent used in leather industry

The development of new tanning agents and new technologies in the leather sector is required to cope with the increasingly higher environmental pressure on the current tanning materials and processes such as tanning with chromium salts. In this paper, the use of titanium wastes (cuttings) resulting from the process of obtaining highly pure titanium (ingots), for the synthesis of new tanning agent and tanning bovine hides with new tanning agent, as alternative to tanning with chromium salts are investigated. For this purpose, Ti waste and Ti-based tanning agent were characterized for metal content by inductively coupled plasma mass spectrometry (ICP-MS) and chemical analysis; the tanned leather (wet white leather) was characterized by Scanning Electron Microscope/Energy Dispersive Using X-ray (Analysis). SEM/EDX analysis for metal content; Differential scanning calorimetric (DSC), Micro-Hot-Table and standard shrinkage temperature showing a hydrothermal stability (ranged from 75.3 to 77 °C) and chemical analysis showing the leather is tanned and can be processed through the subsequent mechanical operations (splitting, shaving). On the other hand, an analysis of major minor trace substances from Ti-end waste (especially vanadium content) in new tanning agent and wet white leather (not detected) and residue stream was performed and showed that leachability of vanadium is acceptable. The results obtained show that new tanning agent obtained from Ti end waste can be used for tanning bovine hides, as eco-friendly alternative for chrome tanning.