Separating Pro-Environment Technologies for Waste Treatment, Soil and Sediments Remediation

The use of mineral processing techniques, such as size classification, attrition, gravity separation, flotation etc., can be considered attractive to treat contaminated waste when there is the possibility to recover marketable materials and/or to reduce drastically the volume and the contaminants of the rejects to be located in controlled waste disposal sites. This paper gives some examples of their application to treat: a mine waste contaminated with heavy metals; a granite waste, a contaminated sediments dredging and fly ash from a coal power station.

Packaging waste are commonly used as new raw materials reducing the depletion of natural resources. The separation between the different materials is mandatory if the application in high value added products is desired. Today, one challenge for recycling is the separation of shredded polymers with approximate density. In this chapter the specific problems related with the separation of PS (Polystyrene) from PET (Polyethylene Terephthalate) and PVC (Polyvinyl Chloride) are addressed.

The most important international literature describing experimental studies are reviewed and a summation of the experimental work supervised by the author is presented. The application of gravity concentration and froth flotation is proposed. The results of the experimentation carried out with representative samples of post-consumer packaging plastics at laboratory scale and in a pilot plant continuously operated are presented. The study confirmed the process feasibility but highlighted some difficulties and limitations.

MSWI-bottom-ash (IBA) and C&D-waste (CDW) are notoriously difficult to classify or separate at grain sizes below 12 mm. The problem is caused by the combined presence of (-1 mm) fines and moisture, which act together to form agglomerates and foul screens and other separation equipment. Results are presented of an experimental study into the separation performance of a new type of classifier, called Advanced Dry Recovery (ADR), which is designed to deal with fine moist materials. The study focused on IBA and two types of CDW: crushed concrete and sieve sand. For each of these three materials, the particle size distribution and moisture content of the fine and coarse ADR products were analyzed. It was found that more than 80% of the fines of the input materials is recovered into the fine product. For IBA, the reduction of fines in the coarse product resulted in more than double of the -8 mm non-ferrous metal recovery at the downstream eddy current separators. The coarse products from crushed concrete showed sufficiently low levels of cement fines, wood and foams to consistently satisfy the European norm for secondary aggregates and avoid problems with caking in storing this material. In a final experiment, about 23% of sieve sand was reclaimed as reusable aggregate.

Sensor based sorting consists of the separation of single particles on the basis of identifiable material attributes that can be measured by suitable detectors. This technique has revolutionized the design of mechanical treatment processes especially in the field of dry waste separation systems. The complexity and the number of sensors are the main determinative factors influencing the separation results. Today, newly developed devices are often equipped with a combination of different sensors in order to recognize multiple material properties in a single step, whereas, the sensor data are evaluated in real-time by a computer system. As a consequence, these devices guarantee excellent separation efficiencies in comparison with those having single sensors. Additionally, the advancing development of new sensor systems makes new fields of application in waste treatment accessible.

Post-consumer steel scrap resulting from End-of-Life Vehicles (ELV), Waste from Electric and Electronic Equipment (WEEE) and Incineration Bottom Ash (IBA) is often hand picked for copper, stone, cloth and other contaminants, in order to meet the specifications of the steelmakers. At capacities of 20 t/h of scrap or more, the efficiency of hand sorting generally becomes problematic, hence, leaving half of the copper in the steel product. New technologies are presently being proposed to facilitate or even eliminate hand sorting of these types of scrap, allowing operators to increase revenues from copper, expand plant capacity, realize a higher and more consistent steel product quality or avoid legal constraints associated with hand pickers. A shape-sensitive magnetic separator called “Clean Scrap Machine” (CSM) pre-sorts the scrap into a bulky thin-walled steel fraction of consistently high purity and a volumetrically much smaller flow of relatively heavy parts in which the contaminants are concentrated. The latter flow can either be sorted by a much smaller number of hand pickers, by sensor sorting, or it can be sold directly to specialized sorters to extract the copper. Detailed results are reported for mid-sized IBA scrap.

The exponential growth of photovoltaic (PV) installations highlights the necessity to cope with the environmental impacts which could raise from wrong practices for disposal of end-of-life PV modules. In fact, their possible disposal in landfills would represent a loss of materials and energy, as PV modules are goods that can become very useful even at the end of their life.

In order to improve the valorisation of waste coming from end-of-life PV modules and of materials they contain, high value recycling processes are needed. These solutions differ from other end-of-life management alternatives, that are generally more simple and economical, like for example the treatment of the PV modules in a recycling plant for laminated glass or their disposal at a landfill after the recovery of the aluminium frame and a pre-treatment in a municipal incineration plant. All these low value approaches have in common the loss of valuable resources, represented by high value materials and components contained in PV modules (wafer/silicon, indium, tellurium and so on), which inevitably would end their life cycle in a landfill, without being adequately recovered.

Differently, some separation and treatment processes have been recently developed, adopting machines and also plants deriving from traditional mineral processing, which allow recovering and recycling of precious metals and materials.

The recycling of e-waste in general allows the recovery of valuable materials, which can be reused as secondary raw materials. However this implies, to adopt reliable treatment processes to achieve specific standard characteristics. Actually, the market standards are very strict and strongly affect the economic value of recovered materials.

In particular, waste refrigerators recycling allows the recovery of different plastic materials and metallic fractions (ferrous and non ferrous), whose economic value has considerably increased in the last years. Only in Italy, in 2010, approximately 66,000 tons of waste refrigerators were collected for recycling. An efficient recycling treatment could assure about 85% of recovery rate.

In this paper, a model to control and characterize the materials recovered from mechanical recycling of carcasses dismantled from waste refrigerators is proposed. The treatment flow sheet consists of various separation and comminution operations. A mathematical model was implemented to determine a partition function, utilizing data obtained from the treatment of 100 waste refrigerator carcasses, carrying out mass balance of recovered materials. The partition function was used to determine control parameters and assess the quality of the recovered products, and, therefore, of the applied technologies. The results have shown that for waste refrigerator carcasses it has been possible to reach for ferrous metals a recovery rate of 97.5% with purity of more than 98%. Other metals also reached a good quality (about 87% for non-ferrous metals, 92% for mixed recyclable plastics), but with lower recovery rates.

When dealing with contaminated sites, one of the main problems to be faced is the treatment of groundwater. In fact, in order to contain the contamination and to remediate the site, a common managing and operational option is to extract the groundwater and treat it at the surface prior to discharge. This remedial strategy is referred to as conventional pump-and-treat technology and its purpose is to remove or reduce contaminants concentrations so that, after the discharge of the treated water, the receiving waters meet the relevant quality objectives and provisions required by local or national regulations, directives or standards. Towards this aim, in the present research work, a matrix based approach has been adopted for modelling a treatment process for contaminated groundwater. In particular, it has been considered a modified Broadbent and Callcott breakage-matrix whose elements have been replaced by first-order kinetic equations that represent the depletion rate of contaminants’ concentrations. The adopted approach allows determining the proper recirculation ratio in a groundwater treatment process for achieving the water quality objectives for discharge. Field tests have been conducted for the setting up of the mathematical model to be used for the revamping of an evaporating tower. The results of chemical analyses carried out on groundwater samples, collected in the input and the output flows of the evaporative tower, confirmed the effectiveness of the proposed approach.

Industrial wastewaters such as mining effluents and landfill leachate may contain metal ions in higher concentrations than those for which the regulatory standards require a treatment for their removal/reduction. Chemical precipitation/settling is the most common method used for removal/reduction of metal ions (e.g. iron, lead, copper, nickel, zinc, aluminum, manganese, etc.). Separation of metalloids (e.g. arsenic, selenium, molybdenum, antimony, etc.) can be achieved by co-adsorption onto iron or aluminum. Thiosalts, incomplete anoxysulphur compounds and cyanide often require the addition of a strong oxidation reagent. Biological nitrification and denitrification are conventional methods for removal of ammonia and nitrate. Respectively as industry accepts and often prefers to use conventional methods as proven and best available technology economically achievable (BATEA), depending on the site conditions and requirements. Emerging technologies such as membrane technologies (e.g. nanofiltration, reverse osmosis, etc.) have only been recently applied to many sites. Innovative approaches, such as snow making, are also used to separate ammonia and metal ions from wastewaters. Innovations have progressed on developing either new technologies or new approaches for mode of application of known technologies. Mode of application could vary from active methods, where pumps and pipes are used and the process takes place in reactors under controlled conditions, or passive methods, where the use of pipes and pumps is eliminated or limited. Wetlands (natural or engineered) and peat filters are often considered as passive methods. Conventional, emerging and innovative separation technologies and application of passive and active methods as well as capabilities and limitation of processes are discussed.

Sediments that are dredged during routine operations for maintenance of harbour areas are generally contaminated, even in consideration of given standards or regulations that do not allow their free disposal in the aquatic system. Therefore, sediments coming from dredging operations have to be properly characterised since their final destination depends on the level of contamination.

Due to the quantity of dredged sediments and the number of contaminants to determine, analyses carried out for characterisation are expensive and time-consuming.

In this research work, a new approach for a prompt evaluation of sediments’ contamination based on hyperspectral analysis is proposed. Results of laboratory tests carried out on marine sediments, before and after chemical-physical treatments, show a correlation among the value of reflectance, obtained by hyperspectral analysis, and the level of contamination and size distribution of sediments.