Characteristics of trace elements and potential environmental risks of the ash from agricultural straw direct combustion biomass power plant

Elements characteristics and potential environmental risk assessment of jarosite residue and arsenic sulfide residue based on geochemical and mineralogical analysis

The waste slag known as jarosite residue (JR) and arsenic sulfide residue (ASR) were produced following the creation of zinc by hydrometallurgical procedures. The increasing annual zinc mining has led to growing pressure to dispose of the resulting JR and ASR from zinc smelting, making it crucial to assess their environmental impact and feasibility for utilization. The main components, distribution characteristics of elements, and potential environmental risks of zinc smelting wastes are studied through toxicity leaching tests, sequential extraction procedures, and various characterization technologies such as XRF, XRD, and SEM-EDS. The mineral compositions of JR are natrojarosite, franklinite, and gunningite, and zinc mainly adheres to the crevices of the natrojarosite mineral. Meanwhile, the ASR of flocculent structures is composed of orpiment, greenockite, arsenic oxide, and calvertite, and As appears in the form of the S-As-O phase. The Zn, Cu, and Cd in JR were dominated by exchangeable bound (81.53-96.6 %), and the main form of As, Cd, Se, and Tl in ASR was organic matter bound (87.0-99.21 %). The Risk Assessment Code (RAC) method confirmed the risk of Cd, Cu, Zn, and Mo in JR is high, while the risk of Cd, Pb, and Cr in ASR is moderate. Compared to the standard value of "Identification Standard for Toxicity of Hazardous Waste Leaching (GB5085.3-2007)", the leachate concentrations of Zn in JR as well as Cd and As in ASR were exceeded, suggesting that the JR and ASR were in the type of hazardous waste and posed an environmental risk. The study provides theoretical guidance for the future rational management and effective utilization of hazardous waste.

Straw pyrolysis for use in electricity storage installations

A concept has been proposed for an installation designed to store excess electricity periodically occurring on the grid. Excess electricity will be used for straw pyrolysis. The main pyrolysis product, gas, will be used to generate electricity using a combustion generator to feed back power into the grid during periods of shortage. The resulting biochar from the pyrolysis can be introduced into the soil to improve soil quality and play a significant role in carbon sequestration. The system uses an electrically heated reactor with a screw conveyor. To preliminarily assess the feasibility of this system, experiments were carried out using wheat straw at temperatures of 300, 400, 500, 600, and 700 °C for the pyrolysis reactor. The resulting gas-to-feedstock mass ratio ranged from 29.04 % at 300 °C to 52.7 % at 700 °C reactor temperature, the biochar mass yield ratio to feedstock varied from 39.41 % to 27.36 % (at 700 °C), and the pyrolysis liquid ranged from 31.55 % to 27.36 % (at 700 °C). The pyrolytic liquid contained a high water content relative to its mass, reaching up to 95.2 % at 700 °C, rendering it less suitable as an energy feedstock. At a reactor temperature of 700 °C, the energy value of the gas produced from the feedstock was twice that of the electricity used for the pyrolysis process. These results suggest the feasibility and operation of the proposed installation.

Chemical Speciation, Leaching Behavior, and Environmental Risk Assessment of Trace Elements in the Bottom Ash from Biomass Power Plant

Biomass combustion for power generation stands as a pivotal method in energy utilization, offering a promising approach for renewable energy utilization. However, the substantial volume of slag produced by biomass burning plants poses environmental challenges, impeding sustainable energy practices. This article systematically studies the characteristics of ash generated from typical biomass direct combustion power plant ash and analyzes the chemical composition, trace element content characteristics, leaching characteristics, and chemical forms of biomass bottom ash. Furthermore, it assesses the environmental ecology and bioavailability of trace elements in bottom ash using the ecological risk assessment method and RAC method. The results demonstrate that the biomass bottom ash contains plant nutrients, such as K, Ca, Mg, and P, while the content of harmful trace elements is lower than the relevant Chinese standards. In dissolution experiments, the leaching rate of nearly all elements remains exceptionally low, primarily due to the distribution of trace elements within the lattice structure of stable minerals. Trace elements predominantly exist in the residual phase, Cu and Zn primarily found in organic compounds and sulfide bound states, while other elements mostly exist in the form of iron manganese oxide bound states. Ecological risk assessment indicates a significant risk level for Cd, contrasting with the slight risk associated with other elements. RAC results indicated no ecological risk of all of the trace elements. Consequently, the utilization of bottom ash in agricultural and forestry soils is deemed to be viable. These findings serve as a crucial foundation for biomass bottom ash resource utilization and underpin the sustainable utilization of biomass energy.

Concentration, speciation and risk effects of multiple environmentally sensitive trace elements in respirable fine-grained fly ash

Respirable fine-grained fly ash (RFA) is captured very inefficiently by existing air purification devices of power plant, leading to increasing concerns regarding their migration and subsequent interaction with body due to fine particle size and its complex toxic composition. Trace elements of RFA in three groups with five different sizes between 8-13 µm were analyzed in terms of available concentration, speciation and risk effects. The concentration, pollution level and ecological risk level of elements in RFA were related to particle sizes. Chronic non-carcinogenic effect risk (NER) and carcinogenic effect risk (CER) were negatively correlated with particle size. The individual weight of exposed subjects, corresponding trace elements concentration and ingestion rate in RFA were three significant variables influencing CER. NER and CER had a tenfold exaggerated effect when calculated using total element concentration of RFA. In addition to individual differences and exposure conditions, trace element properties, speciation and available concentration were the dominant factor responsible for ecological and environmental effects of trace elements in RFA, following the order As>Ni, Mn>Cr>Pb>Cu>Zn. Results of this work highlight the effects and differences of trace elements in RFA on ecology and health, and provide a basis for further pollution control and human health warning.