Zinc recovery from Waste-to-Energy fly ash – A pilot test study

Zinc recovery from MSWI fly ash using acidic leaching and chemical precipitation was studied at pilot scale. The leached fly ash was re-incinerated in order to destroy toxic dioxins. 75–150 kg/h of fly ash from a Swedish Waste-to-Energy plant was mixed with scrubber liquids from the same flue gas treatment system in a continuously stirred vessel. The resulting slurry was dewatered in a vacuum belt filter. Hydroxide precipitation of the produced leachate, at a pH of around 9, followed by filtration of the formed crystals in a membrane filter press produced a filter cake with up to 80 wt% Zn(OH)2 in dry solids, calculated from Zn(tot). Up to 70% of the zinc content in the fly ash could be recovered. Two 4-hour full scale ash re-incineration tests were performed: leached fly ash was mixed with the waste at a ratio corresponding to a situation where all the fly ash was continuously re-incinerated. The tests showed only an 8% mass increase of produced fly ash, which means that most of it ended up in the bottom ash, although some elements could potentially accumulate in the system if all the fly ash was to be continuously re-incinerated. No negative effects were observed on the bottom ash quality, which suggests that a large portion of the toxic fly ash could be transformed into the bottom ash fraction

Combined wastewater treatment and recovery of copper from ash leachate

Ashes from incineration of municipal solid waste contain metals, such as copper and zinc, in high concentrations. The metals can be leached out from the ashes using acids and recovered by electrolysis. To lower the energy demand of the electrolysis step, we have investigated a bioelectrochemical system for combined wastewater treatment and copper recovery from simulated ash leachate. Bacteria at the anode oxidize wastewater organics and produce a current that flows through an external circuit to the cathode, where copper is reduced and recovered. We tested a bioelectrochemical system with carbon anode and titanium cathode. With a cathode potential poised at -0.3 V, the energy required for copper reduction was reduced from 1.46 kWh/kg Cu with an abiotic anode compared to 0.23 kWh/kg Cu with a biological anode oxidizing acetate. With a cathode potential of 0.1 V, electrical energy could be recovered from the system together with copper

Metals in MSWI fly ash - problems or opportunities?

Incineration of municipal solid waste is a commonly used management method to take care of our waste. However, the residues produced are a problem. They often contain large amounts of potentially toxic metal compounds and soluble salts, which can cause harm to the environment and human health if released from the ash. These ashes are therefore usually classified as hazardous materials and are deposited in specialized landfills. However, as society strives towards more sustainable material cycles, a larger fraction of the materials today classified as waste will, in the near future, be recycled. Since the ashes produced from waste incineration contain significant amounts of metals, they represent a possible source of these metals. Recovery of metals from waste combustion residues would thus give an opportunity to turn a waste into a valuable resource. This thesis focuses on the leaching and recovery of minor metals, such as Cu and Zn, and proposes a recovery procedure for Cu. The leaching of metal compounds from the ash is a very important step in the recovery process and several factors, such as leaching time, pH, leaching agent used and the liquid-to-solid ratio (L/S), affect the leaching properties. In some cases more or less all Cu was leached from the ash. Recovery of metals from ash leachates can be done using solvent extraction, and the results obtained showed that about 90% of the Cu in the leachates could be selectively recovered. The ash matrix itself is highly affected by leaching, which generally increases the specific surface area and changes the particle size distribution. In landfill leaching tests the release of many ions from pre-leached ash was lower than that measured for the original ash, indicating a possibility to utilize the resulting ash as well

Speciation of Cu and Zn in bottom ash from solid waste incineration studied by XAS, XRD, and geochemical modelling

Millions of tons of bottom ash (BA) is generated from incineration of industrial and municipal solid waste each year within EU. The magnitude of leaching of metals like Cu and Zn is critical for hazard and risk assessment of these ashes. Although speciation of metals is a key factor to understand and predict metal leaching, speciation of Cu and Zn in BA is not well known. In this study six metal separated and carbonized BA were investigated by a combination of X-ray absorption spectroscopy, X-ray diffraction, leaching/extraction tests, and geochemical modelling. Five of the BA were from grate boilers and one from a fluidized bed incinerator. The aims were to identify similarities in Cu and Zn speciation and to identify main species. The combination of several techniques was necessary to draw conclusions about speciation and displayed coherent results. A similar speciation of Cu and Zn was indicated in the five studied grate boiler ashes although the proportions between species may vary. Copper(II) oxide and Cu metal were the main Cu species in all BA. Zinc(II) oxide and willemite (Zn2SiO4) were identified in grate boiler ashes. The fluidized bed ash contained Zn-Si-minerals and possibly franklinite or gahnite, while the Zn(II) oxide content was low, if any. The results have implications for classification and risk assessment of MIBA. (C) 2020 The Authors. Published by Elsevier Ltd

Initial study on phytoextraction for recovery of metals from sorted and aged waste‐to‐energy bottom ash

Sorted and aged bottom ash from Waste‐to‐Energy plants, i.e., MIBA (the Mineral fraction of Incinerator Bottom Ash) are potential source of metals that could be utilized to meet the increased demand from society. In this work, sunflowers (Helianthus annuus) and rapeseed (Brassica napus) were cultivated in conventional MIBA to evaluate the possibility for phytoextraction, mainly of Zn, during the period of one cultivation season in the Nordic climate. The results show that metal extraction from MIBA using rapeseed and sunflowers is workable but that neither of the used plants is optimal, mainly due to the inhibited root development and low water‐ and nutrient‐holding capacities of MIBA. The addition of fertilizer is also important for growth. There was a simultaneous accumulation of numerous metals in both plant types, and the highest metal content was generally found in the roots. Calculations indicated that the ash from rapeseed root incineration contained about 2% Zn, and the contents of Co, Cu, and Pb were comparable to those in workable ores. This initial study shows that cultivation in and phytoextraction on MIBA is possible, and that the potential for increased metal extraction is high

Leaching for recovery of copper from municipal solid waste incineration fly ash: Influence of ash properties and metal speciation.

Recovery of metals occurring in significant amounts in municipal solid waste incineration fly ash, such as copper, could offer several advantages: a decreased amount of potentially mobile metal compounds going to landfill, saving of natural resources and a monetary value. A combination of leaching and solvent extraction may constitute a feasible recovery path for metals from municipal solid waste incineration fly ash. However, it has been shown that the initial dissolution and leaching is a limiting step in such a recovery process. The work described in this article was focused on elucidating physical and chemical differences between two ash samples with the aim of explaining the differences in copper release from these samples in two leaching methods. The results showed that the chemical speciation is an important factor affecting the release of copper. The occurrence of copper as phosphate or silicate will hinder leaching, while sulphate and chloride will facilitate leaching

Life Cycle Assessment of Phosphorus Sources from Phosphate ore and urban sinks: Sewage Sludge and MSW Incineration fly ash

Urban sinks accumulate phosphorus and other elements and may serve as sources of secondary raw materials. This paper evaluates phosphorus sources based on their environmental impact. In a life cycle assessment (LCA) the conventional production was used as a yardstick against which tomeasure the performance of two recycling options: spreading of sewage sludge and phosphorus recovery from municipal solid waste incineration fly ash (MSWA). When compared as three gate-to-gate processes, the sludge spreading had the lowest potential environmental impact, except in the impact categories eco- and human toxicity. In the future, the sludge spreading could potentially outperform the conventional process also with regard to toxicity, provided its Hg and Cu content can be reduced. Phosphorus extracted from the MSWA had the highest impact, except in relation to eutrophication. The benefits of avoiding the conventional production were greater than the sludge recycling impacts for all categories except toxicity. When conventional production is substituted by the MSWA recycling, the eutrophication and land-use impacts are avoided, while the impacts in other categories are considerable. The development needs identified for this method include substitution of HCl, reduced water consumption, and reduction of the product’smetal content. Solutions to all of these challenges have been proposed and are currently being tested

Initial studies of the recovery of Cu from MSWI fly ash leachates using solvent extraction

Large volumes of ash from combustion of municipal solid waste are produced and most of it is landfilled. As this type of ash contains significant amounts of metal compounds the landfilling strategy is not optimal when considered from a resource conservation perspective. A better situation would be created if metals were recovered from the ash. In the present study leaching and solvent extraction was applied for release and separation of copper from municipal solid waste combustion fly ashes. The results showed promising results with Cu yields of 50-95%. The yield was heavily dependent on the efficiency of the initial leaching of Cu from the ash

Low impact leaching agents as remediation media for organotin and metal contaminated sediments

All over the world, elevated levels of metals and the toxic compound tributyltin (TBT) and its degradation products are found in sediments, especially close to areas associated with shipping and anthropogenic activities. Ports require regular removal of sediments. As a result, large volumes of often contaminated sediments must be managed. The aim of this study was to investigate enhanced leaching as a treatment method for organotin (TBT) and metal (Cu and Zn) contaminated marine sediments. Thus, enabling the possibility to reuse these cleaner masses e.g. in construction. In addition to using acid and alkaline leaching agents that extract the OTs and metals but reduce the management options post treatment, innovative alternatives such as EDDS, hydroxypropyl cellulose, humic acid, iron colloids, ultra-pure Milli-Q water, saponified tall oil (“soap”), and NaCl were tested. Organotin removal ranged from 36 to 75%, where the most efficient leaching agent was Milli-Q water, which was also the leaching agent achieving the highest removal rate for TBT (46%), followed by soap (34%). The TBT reduction accomplished by Milli-Q water and soap leaching enabled a change in Swedish sediment classification from the highest class to the second highest class. The highest reduction of Zn was in HPC leached samples (39% removal) and Cu in EDDS leached samples (33% removal). Although high metal and OT leaching were achieved, none of the investigated leaching agents are sufficiently effective for the removal of both metals and OTs. The results of this study indicate that leaching with ultra-clean water, such as Milli-Q water, may be sufficient to treat TBT contaminated sediments and potentially allow mass reuse

Integrated assessment of management strategies for metal-contaminated dredged sediments – What are the best approaches for ports, marinas and waterways?

Sediments in ports, marinas and waterways around the world are often contaminated with metals arising from anthropogenic activities. Regular dredging is needed to achieve an appropriate water depth and reduce the environmental impact of pollutants. The aim of this study was to develop an integrated assessment method for comparing various management strategies for dredged sediments at six case study sites in Sweden. Short- and long-term environmental impacts were investigated for different management approaches, including landfilling, deep-sea disposal, metal extraction in combination with the two aforementioned, and natural recovery (no dredging). The potential value of metals in the sediments was estimated using sediment metal contents and current metal prices. Additionally, an assessment of how metal extraction could result in lower management costs was carried out. The cost of the different management approaches was calculated and evaluated together with the corresponding environmental impacts. This study shows that there is a monetary value in dredged materials, in terms of metal content, and that the materials can potentially be used for metal extraction. Metal extraction may also help to reduce the management costs, as cleaner materials are cheaper to handle. The choice of metal recovery method is important in both monetary and environmental terms, potentially contributing to a circular economy. In the future, metal recovery may become more profitable, as technologies are improved, and due to probable increases in metal prices and landfill costs