The formation of gold in woody biomass combustion ashes.

This paper investigates the enrichment of gold through combustion and ash-leaching techniques utilizing woody biomass as a fuel source. It delves into the formation of gold in ashes derived from the fixed grate combustion of pelletized woody biomass containing noble metals, conducted at a pilot-scale boiler. The biomass sample was gathered from a brownfield land at an abandoned mining area, avoiding induced phytoextraction. The fuel contained <0.05 mg/kg gold, while the bottom ash, after heat exchanger ash, deposited ash, and fly ash contained 1.52 mg/kg, 1.99 mg/kg, 2.64 mg/kg, and 3.52 mg/kg of gold, respectively. Although the amount of fly ash is lower compared to bottom ash, the concentration of gold is the highest in fly ash, which follows the after heat exchanger ash and bottom ash. The concentration of gold was enriched by a three-stage procedure of water leaching, acid leaching (10 % HCl), and alkaline leaching (5 % NaOH), after which 12.1 mg/kg and 12.6 mg/kg gold was found in the residues obtained from leached bottom ash and deposited ash, respectively. SEM was utilized to depict the morphology of gold, which appears in bottom ash as individual neat particles with a purity higher than 98 %. Pure gold particles in the size of 1-2 µm are presented in the after heat exchanger ash; meanwhile, gold in fly ash is primarily associated with potassium, sodium, sulfur, and oxygen. The findings in this study pave the way for reclaiming gold from bio-ores as well as assist in better understanding the formation of this precious metal in these secondary resources.

The fate of noble metals and rare earth elements during pelletized biomass combustion.

The extraction of rare earth elements (REEs) and noble metals (NMs) from unconventional resources is playing a crucial role under the context of industrialization and reserve depletions. Plants used for phytoextraction are promising materials for the recovery of metals, but the biomass needs to be reduced to a manageable amount and volume prior to the extraction process. This paper investigates the combustion process of biomass focusing on NMs and REEs flow. The plants harvested from a brownfield land were pelletized and incinerated in a fixed-grate pilot-scale boiler, meanwhile, solid remains from various points in the combustion and flue gas system were captured and analyzed. The results show that levels of NMs in deposited ash and fly ash are greater than in bottom ash. Meanwhile, the higher REE concentration in bottom ash compared to that in other solid residuals demonstrates the less ability of these compounds to escape from the combustion chamber. Generally, the concentrations of REEs and NMs in the solid residues are significantly higher compared to biomass. SEM-EDS analyses of the contaminated solid remains indicate that gold forms individual particles with purity higher than 95 wt% in the bottom ashes, and this finding adds novel insights into gold phytomining.

Phytomining of rare earth elements - A review.

The increasing demand for rare earth elements (REEs) for modern industry has led to a surge in mining activities and consequently has released these metals into the environment. Intensifying REEs in a habitat has impacts on its ecosystem, but on the other side, it also provides the opportunity to recover REEs from low-grade minerals. Phytomining has emerged as an ecologically sound technique to extract these valuable elements from contaminated soils where traditional mining is not competitive. This paper presents and reviews the concept of REE phytomining from three scientific areas. The accumulation of rare earth metals in plants is the first stage, referred to as the phytoextraction process. This is followed by elevating REE concentrations into bio-ores via the enrichment phase. Ultimately, extraction is the final step to complete the phytomining pathway for reclaiming REEs in brownfield land.

Phytomining of noble metals - A review.

Phytomining of noble metals (NMs) offers a promising possibility of metal extraction at sites where traditional mining activities or recovering NMs from low-grade minerals are not competitive. In addition to conventional mining, producing NMs from secondary resources strengthening the circular economy has been paid worldwide attention. The review presented in this paper links three scientific areas as the essential elements to form the phytomining chain of NMs. The accumulation of NMs in plants is the first step, referred as the phytoextraction process. This is followed by heightening the concentration of NMs via the enrichment stage. Eventually, although less well understood, extraction methods of NMs from biomass solid remains as well as from diverse secondary sources particularly incineration ashes are discussed that assist to visualize the potential pathways in phytomining.

Disposal options for polluted plants grown on heavy metal contaminated brownfield lands - A review.

Reducing or preventing damage caused by environmental pollution is a significant goal nowadays. Phytoextraction, as remediation technique is widely used, but during the process, the heavy metal content of the biomass grown on these sites special treatment and disposal techniques are required, for example liquid extraction, direct disposal, composting, and combustion. These processes are discussed in this review in economical and environmental aspects. The following main properties are analyzed: form and harmful element content of remains, utilization of the main and byproducts, affect to the environment during the treatment and disposal. The thermal treatment (combustion, gasification) of contaminated biomass provides a promising alternative disposal option, because the energy production affects the rate of return, and the harmful elements are riched in a small amount of solid remains depending on the ash content of the plant (1-2%). The biomass combustion technology is a wildely used energy production process in residential and industrial scale, but the ordinary biomass firing systems are not suited to burn this type of fuel without environmental risk.

Investigation of natural gas theft by magnetic remanence mapping.

Natural gas theft causes major losses in the energy industry in Hungary. Among the non-technical losses occurring in natural gas networks, fraudulent residential consumption is one of the main factors. Up to 2014, gas meters that are most widely used in residential monitoring are manufactured with ferromagnetic moving components, which makes it possible to alter or disrupt the operation of the meters non-intrusively by placing permanent magnets on the casing of the meters. Magnetic remanence mapping was used to investigate a sample of 80 recalled residential meters and detect potentially fraudulent activity. 10% of the meters were found suspect by magnetic remanence measurement, of which 50% were confirmed to be potentially hijacked by further mechanical investigation. The details of the technique are described in this paper, along with experimental results and the discussion of the analysis of the real-world samples.

Solubility analysis and disposal options of combustion residues from plants grown on contaminated mining area.

Biomass, as a renewable energy source, is an excellent alternative for the partial replacement of fossil fuels in thermal and electric energy production. A new fuel type as biomass for energy utilisation includes ligneous plants with considerable heavy metal content. The combustion process must be controlled during the firing of significant quantities of contaminated biomass grown on brownfield lands. By implementing these measures, air pollution and further soil contamination caused by the disposal of the solid burning residue, the ash, can be prevented. For the test samples from ligneous plants grown on heavy metal-contaminated fields, an ore mine (already closed for 25 years) was chosen. With our focus on the determination of the heavy metal content, we have examined the composition of the soil, the biomass and the combustion by-products (ash, fly ash). Our results confirm that ash resulting from the combustion must be treated as toxic waste and its deposition must take place on hazardous waste disposal sites. Biomass of these characteristics can be burnt in special combustion facility that was equipped with means for the disposal of solid burning residues as well as air pollutants.