Bioleaching Treatment Research Articles

Promoting dewatering efficiency of sludge by bioleaching coupling chemical flocculation

In recent years, bioleaching has emerged as a cost-effective technology for enhancing the dewaterability of sludge. However, the lengthy treatment time involved in sludge bioleaching processes limits daily treatment capacity for sludge. Here, a novel approach was developed through a short time of sludge bioleaching with A. ferrooxidans LX5 (A. f) and A. thiooxidans TS6 (A. t) followed by polyferric sulfate (PFS) flocculation (A. f + A. t + PFS). After 12.5 h of the A. f + A. t + PFS treatment (30% A. f, 10% A. t, 40 mg/g DS S0, 60 mg/g DS FeSO4•7H2O, and 120 mg/g DS PFS), the reduction efficiency of specific resistance to filtration (SRF) and sludge cake moisture content reached 94.0% and 11.6%, respectively, which were comparable to the results achieved through 24 h of completed bioleaching treatment. In pilot-scale applications, the mechanical dewatering performance was notably improved following A. f + A. t + PFS treatment, with the low moisture content of the treated sludge cake (∼59.2%). This study provides new insights into the A. f + A. t + PFS process and holds potential for developing efficient and promising sludge dewatering strategies in engineering application.

Column Bioleaching of Nickel from Sulfidic Samples with Different Nickel and Magnesium Content

Nickel is a valuable metal that is becoming more prevalent in the industry. Column bioleaching was used in this study to extract nickel from magnesium-bearing sulfide minerals. Two different sulfidic samples with different nickel and magnesium content were utilized to investigate the performance of column bioleaching. It was discovered that mesophilic cultures’ adaptation is delayed by increasing magnesium contents. Bioleaching outperformed leaching in terms of recovery by 80% compared to 50% in sample 1 and 70% compared to 40% in sample 2. Jarosite is precipitated in samples with a high magnesium content due to the high pH and oxidation level, which lowers bioleaching effectiveness. The pretreatment method using acid washing before the start of bioleaching treatment can reduce the amount of magnesium in samples, which increases the Ni recovery in both samples. SEM analysis was performed on each bioleaching residue. The result showed that high amounts of magnesium in the second sample could be a factor in the precipitation of jarosite. Finally, it can be concluded that the pretreatment method is a feasible Bio-heap operation.

Effects of complex sulphur substrates on sludge bioleaching to improve heavy metal removal and microbial community diversity

In this study, H2S was used as a partial replacement nutrient substrate for sludge bioleaching. The effects of different combinations of H2S/sludge load and monomeric sulphur on heavy metal removal and microbial communities were investigated. Changes in pH, oxidation-reduction potential (ORP), SO42− concentration, heavy metal removal, and the content of heavy metal states during bioleaching were investigated, and community diversity analysis was performed. Daily introduction of H2S three times (at an interval of 8 h) at a gas flow rate of 2 ml/min and an H2S/sludge load of 15 ml/L with 5 g/L FeSO4·7H2O and 2 g/L monomeric sulphur as a nutrient substrate significantly accelerated both the bioleaching process and the pH drop in the sludge system, promoted the production of SO42−, and maintained a higher redox potential. The combination of H2S and monomeric sulphur had a significant effect on the leaching of heavy metals. Compared with the experimental group containing only H2S or monomeric sulphur, the removal rates of Zn, Ni, Pb, and Cr increased by 4.63%/13.8%, 8.5%/20.07%, 3.84%/9.5%, and 4.24%/8.02% respectively, while promoting the transformation of various heavy metal states to labile states, improving heavy metal stability, and reducing sludge ecotoxicity. High-throughput sequencing analysis showed that introducing the H2S gaseous matrix accelerated the decreasing trend of species number, bacterial abundance, and community diversity in the sludge system, promoting Proteobacteria as the dominant phylum, Acidithiobacillus, Metallibacterium, and Thiomonas as the dominant genera, and improving the bioleaching treatment effect.

Bioleaching of Valuable Elements from Red Mud: A Study on the Potential of Non-Enriched Biomass

Red mud (RM) is the main residue produced by the alkaline extraction of alumina (Al2O3) from bauxite, and it contains valuable metals such as iron (Fe), aluminium (Al), titanium (Ti), magnesium (Mg), manganese (Mn), rare earth elements, etc. This research aimed to investigate the biologically induced leaching of some valuable elements from raw RM without preliminary biomass enrichment and inoculum, simultaneously reducing RM polluting potential and extracting metals for their subsequent recovery within a circular economy-based approach. In addition to the missing inoculum, such an approach is challenging since high RM alkalinity and pH, as well as the absence of any sulphides, constrain the use of the most common biohydrometallurgical techniques. Red Muds from two European locations were tested (RM-I and RM-II, respectively). Bioleaching tests were performed at different temperatures (T = 22 °C and 28 °C; and also 15 °C for RM-II) and solid-to-liquid ratios (S/L = 2%, 5%). A sudden drop in pH from alkaline to constant neutral/acidic values was observed in almost all tests, and such results were attributed to biological activity since abiotic tests did not show any pH decrease. The best results in terms of extraction were achieved with RM-II, in particular for Al, Mg and Mn (17%, 42% and 47%, respectively). At 2% S/L, the highest temperature allowed for a better metal release, while at 5% S/L, the highest extraction of Al, Mg and Ti was observed at 22 °C. As expected, iron was less available to leach at the achieved pH values, as it was mostly present as hematite in both RMs. Finally, the first microbiological characterisation of the autochthonous biomass selected during the bioleaching treatment of RM was provided.

Enhancing sludge dewatering efficiency through bioleaching facilitated by increasing reactive oxygen species

Bioleaching facilitated by iron-oxidizing bacteria is regarded as a promising sludge dewatering method due to excellent dewaterability and low cost. However, a two-days bioleaching time for sludge conditioning decreased its daily treatment capacity. In fact, Fe2+ easily reacts with O2 to produce reactive oxygen species (ROS) with high oxidizing activity. Can bioleaching performed in Fe2+-rich system generate ROS to decompose sludge extracellular polymeric substances (EPS)? Here both contribution of ROS produced in bioleaching to improve sludge dewaterability and the increase of ROS content to shorten sludge bioleaching treatment time were investigated. The introduction of H2O2 in sludge bioleaching treatment (BS+H2O2) to increase ROS could simultaneously improve sludge dewaterability and decrease bioleaching time. Specific resistance to filtration (SRF) and capillary suction time (CST) reduction ratios (90.3% and 80.9%) in BS+H2O2 process were much higher than those in other processes after only 30 min reaction. Mechanisms of improving sludge dewaterability in BS+H2O2 mainly included ROS oxidation and Fe3+ flocculation by analysis of the contribution factors. These findings not only provide an effectively method to promote sludge dewatering efficiency of bioleaching, but also give new sights into the design of cost-efficient processes for improving the sludge dewatering.

Investigation on bio-desilication process of fly ash based on a self-screened strain of Bacillus amyloliquefaciens and its metabolites

Bio-desilication of fly ash containing a large amount of crystalline and amorphous silicate compound by silicate bacteria had the advantages of energy-saving, environment-friendly, and controllable cost. In this study, a bacteria strain with desilication ability on fly ash was isolated from the soil and identified as Bacillus amyloliquefaciens by 16sRNA and named ZGW-12. Through the bio-leaching treatment of fly ash by ZGW-12, it was found that the concentration of Si was 306.26 mg/L and the concentration of Al3+ was 0.5 mg/L in the pulp. The mechanism of bio-leaching using ZGW-12 was investigated by XRD, HPLC, SEM, and FTIR. The organic acid and amino acid in the bacteria culture medium and the pulp were detected, and it was found that the content of the acidic metabolites in the pulp was much larger than that of the bacteria culture medium. The ore sample particles adsorbed a large number of bacteria cells and took place obvious corrosion. The surface of the ore sample undergone hydroxylation reaction, and the diffraction peak of the silicate crystal compound was unchanged. ZGW-12 exhibits good performance in retaining aluminum and extracting silicon aspect. Availability of data and material (data transparency)All data were true and valid.

Effect of ferrous iron loading on dewaterability, heavy metal removal and bacterial community of digested sludge by Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans ILS-2 was adapted in digested sludge and used to treat sludge for dewaterability improvement. Results showed that increasing ferrous iron loading increased sludge dewaterability, but the inoculation of the bioleaching strain had little effect on sludge dewaterability compared to controls without the strain. The total extracellular polymeric substances (EPS) contents of sludges with and without bioleaching treatment were similar except for bioleaching treatment at 10% ferrous iron loading (on sludge total solids) where total EPS was higher with bioleaching treatment. However, bioleaching treatment for 48 h had a notable effect on removal of heavy metals, such as Mn, Ni and Zn, especially at the high loadings of ferrous iron. In the presence of A. ferrooxidans, the removal of Ni, Mn and Zn reached 93%, 88% and 80%, respectively, at a ferrous iron loading of 21%. The sequencing of 16S rRNA genes indicated that increasing ferrous iron loadings to 15% and 21% increased the relative abundance of Acidithiobacillus, Acidocella (with A. ferrooxidans) and Carboxylicivirga (without A. ferrooxidans) but decreased the abundance of Pseudomonas and Acinetobacter after 48 h treatment. This study enhanced the understanding of the correlations between bioleaching treatment of digested sludge, sludge dewaterability, heavy metal removal and bacterial communities.

Estudio comparativo de un proceso químico y un proceso biotecnológico para la remoción de bismuto de concentrados mineros

In 2018, approximately 17.7 billion metric tons of minerals were produced worldwide, which represent a great importance in the industrial sector. However, most of the minerals are bound with metallic elements, which lower the price of the metals of interest. Secondary materials in valuable metal extraction processes can cause various problems in the mining industry, both economic and environmental. This research aimed evaluate two treatments for the reduction of the bismuth concentration in gold and silver mineral concentrates: Bioleaching and co- precipitation with trioxide arsenic treatment, in the first, native microorganisms of the mineral to be treated were used to reduce the concentration of bismuth; in the second, arsenic trioxide was added in order to form a precipitate that contained bismuth.. The results showed that the chemical co-precipitation treatment with arsenic trioxide can decrease the Bi concentration to a greater extent compared to the bioleaching treatment, up to 16% of the initial concentration, in addition to reducing the concentration of other undesirable elements in metals such as antimony and cadmium by 32 and 11% respectively. From this research work, a collaboration of two techniques can be proposed for a higher reduction of concentration and with greater efficiency.

Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities.

In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56-1.58 and 0.34-1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.

Two-step biohydrometallurgical technology of copper-zinc concentrate processing as an opportunity to reduce negative impacts on the environment

Polymetallic concentrates obtained during ore beneficiation pose a significant problem for the mining and metallurgy industry due to an increase in load on subsequent comminution steps and a high loss of metals in slag during smelting. Storage of such slag can lead to pollution of groundwater due to weathering. Biohydrometallurgy is an option for the processing of sulfidic raw materials that has a low impact on the environment. Processing of sulfidic concentrates of copper-zinc ore via bioleaching techniques was studied in this paper. Three mixed microbial cultures of acidophilic microorganisms were enriched from industrial mining sites: two autotrophic mesophilic cultures containing Acidithiobacillus ferroxidans and Leptospirillum spp. (grown at 30 and 35 °C), and a mixotrophic moderate thermophilic culture containing Sulfobacillus thermotolerans, Leptospirillum ferriphilum, as well as the archaea Ferroplasma acidiphilum and Acidiplasma spp. (grown at 40 °C). The autotrophic microbial culture growing at 30 °C was used to generate an iron-containing biosolution for ferric leaching of a copper-zinc concentrate. Zinc and iron extracted into solution faster than copper during high-temperature (80 °C) ferric leaching of the concentrate due to galvanic interactions between minerals, redox conditions of the medium, and differences between mineral oxidation mechanisms. Weight loss of the leach residue was 34.0%, with relative copper content increased by 1.0%, zinc content decreased by 6.18%, and iron content decreased by 15.1%. Biooxidation of ferrous iron in the pregnant leach solution by three microbial cultures was also studied. The most effective culture was moderate thermophilic. The results of studies on the bioregeneration of leaching solutions are relevant to the development of a two-step biohydrometallurgical technology for processing of copper-zinc concentrate with a closed cycle of technological flows. The ferrous iron biooxidation rate by the moderate thermophilic culture reached 20 g L−1 day−1. The leach residue obtained can be considered a high-grade copper concentrate able to be processed via smelting. This bioleaching process would make it possible to reduce pollution of groundwater by some toxic metals stored in slags. An environmentally friendly technology flow sheet for copper-zinc sulfidic ore processing using two-step bioleaching treatment was proposed.

Elevated pH on Bioleaching of Nandan Lead-Zinc Tailings as Building Materials

A series of the experiments were carried out on the Nandan lead-zinc tailings management and one bioleaching method was proposed with the purpose of recovering the valuable metal such as Zn. Firstly, multi-elements analysis was performed to provide theoretical data. Secondly, the effect of the pH on the bacterial growth and Fe2+ oxidation was investigated. The results showed that pH at 2.5 was the optimum for the bacteria. The concentration of the bacteria at pH 2.5 can be up to 9.3×107 cells/mL. Finally, the bioleaching treatment was performed to study the potential of bioleaching the tailings. The data illustrated that the method of bioleaching can extremely recover metals such as zinc from the tailings, which provided novel insights into metal recycling.

Study of physicochemical changes of polluted sediments from Reconquista river basin (Argentina) after remediation processes

The physicochemical properties of sediments and their ability to retain pollutants are affected by both contamination and remediation processes. The aim of this study is to determine structural and physicochemical changes in real sediment contaminated with metals, subjected to bioleaching processes in a previous study. The sediment contaminated with heavy metals and samples of the same sediment treated with different heap leaching tests were used. They were characterised by potentiometric titrations, electrophoretic mobility, organic matter (OM), nuclear magnetic resonance (NMR), volatile solids and sulphides. For contaminated and treated sediment samples, the results of OM, sulphides, volatile solids to 600°, potentiometric titrations and zeta potential values depended on the bioleaching treatment performed previously. The contaminated sediment sample without any bioleaching treatment presented the greatest amount of OM and sulphides. Moreover, metal adsorption isotherms were performed. The contaminated sediment without bioleaching treatment was the one with the highest adsorption capacity. The baseline sample did not present a noticeable adsorption capacity. This study indicates the importance of the contribution of OM and sulphides to sediments and structural and physicochemical studies after remediation treatments.

Study of physicochemical changes of polluted sediments from Reconquista river basin (Argentina) after remediation processes

The physicochemical properties of sediments and their ability to retain pollutants are affected by both contamination and remediation processes. The aim of this study is to determine structural and physicochemical changes in real sediment contaminated with metals, subjected to bioleaching processes in a previous study. The sediment contaminated with heavy metals and samples of the same sediment treated with different heap leaching tests were used. They were characterised by potentiometric titrations, electrophoretic mobility, organic matter (OM), nuclear magnetic resonance (NMR), volatile solids and sulphides. For contaminated and treated sediment samples, the results of OM, sulphides, volatile solids to 600°, potentiometric titrations and zeta potential values depended on the bioleaching treatment performed previously. The contaminated sediment sample without any bioleaching treatment presented the greatest amount of OM and sulphides. Moreover, metal adsorption isotherms were performed. The contaminated sediment without bioleaching treatment was the one with the highest adsorption capacity. The baseline sample did not present a noticeable adsorption capacity. This study indicates the importance of the contribution of OM and sulphides to sediments and structural and physicochemical studies after remediation treatments.

Bioleaching of heavy metals from sewage sludge, direct action of Acidithiobacillus ferrooxidans or only the impact of pH?

The bioleaching process comprises two mechanisms: direct action of the bacteria and indirect effect of low pH. In this work, the effect of bacteria and the effect of low pH on dissolution of the metals were compared. To study these two mechanisms, bioleaching and the chemical treatment were operated simultaneously at the same pH. Results showed that the effect of bacteria played the main role in dissolution of metals, and regarding metal dissolution, there was a significant difference between these two effects. Although the chemical leaching by means of low pH could dissolve metals, the metals are dissolved mainly by the function of the bacteria rather than dissolution because of low pH. Bioleaching could dissolve Cd (71.90%), Mn (92.5%) and Zn (89.14%), whereas the chemical leaching could dissolve Cd (22.03%), Mn (25.06%) and Zn (14.23%). These results indicate that the main cause of metal dissolution during the bioleaching treatment is the unique impact of bacterial activity, which changes the redox state of the metal rendering them to a more soluble form.

Effect of bioleaching on hydrogen-rich gas production by steam gasification of sewage sludge

Effect of bioleaching on hydrogen-rich gas production by steam gasification of sewage sludge was carried out in a lab-scale fixed-bed reactor. The influence of sewage sludge solids concentrations (6–14% (w/v) in 2% increments) during the bioleaching process and reactor temperature (600–900°C in 100°C increments) on gasification product yields and gas composition were studied. Characterization of samples showed that bioleaching treatment, especially in 6% (w/v) sludge solids concentration, led to metal removal effectively and modifications in the physicochemical property of sewage sludge which was favored for gasification. The maximum gas yield (49.4%) and hydrogen content (46.4%) were obtained at 6% (w/v) sludge solids concentration and reactor temperature of 900°C. Sewage sludge after the bioleaching treatment may be a feasible feedstock for hydrogen-rich gas product.

Bioleaching and combined bioleaching/Fenton-like processes for the treatment of urban anaerobically digested sludge: Removal of heavy metals and improvement of the sludge dewaterability

Abstract The objective of this study was to compare the performances of bioleaching and combined bioleaching/Fenton-like processes for the treatment of urban anaerobically digested sludge. The removal of heavy metals in very low concentrations as well as the improvement of the sludge dewaterability were investigated. The bioleaching treatment based on indigenous microorganisms activity was performed during 18 days and it led to a removal of Cd, Cr, Cu, Pb, and Zn of 81.5% ± 2.5%, 9.9% ± 1.7%, 93.7% ± 7.2%, 33.6% ± 1.0%, and 93.8% ± 3.6%, respectively. It was also shown that the bioleaching process had a significant impact on the sludge dewaterability, since the sludge volume index (SVI) decreased by 55.3%, and the specific cake resistance (SCR) and capillary suction time (CST) were reduced by 94.8% and 97.3%, respectively. Bioleaching was then used as a pre-treatment step and involved in the combined bioleaching/Fenton-like process. Bioleaching used as a pre-treatment was shortened to 6 days, and the Fenton-like reaction was then investigated with the addition of 36 mM, 180 mM and 360 mM H 2 O 2 . The removal of Cd, Cr, Cu, Pb and Zn reached respectively 34.8% ± 0.1%, 14.5% ± 0.1%, 86.3% ± 0.6%, 30.9% ± 1.0% and 97.9% ± 2.4%. The combined bioleaching/Fenton-like process led to a very high improvement of the sludge dewaterability. Indeed, the SVI of the raw sludge was reduced by 62.0%, and SCR and CST decreased by 99.5% and 98.4% respectively. The combination of bioleaching with Fenton-like reaction thus gave promising results for the treatment of sludge in terms of heavy metals removal and improvement of its dewaterability.

The effect of bioleaching on sewage sludge pyrolysis

The effects of bioleaching on sewage sludge pyrolysis were studied. Sewage sludge was treated by bioleaching with solid concentrations of 6% (w/v), 8% (w/v), 10% (w/v). Results showed that bioleaching treatment could modify the physicochemical properties of sewage sludge and enhance the metals removal. The optimum removal efficiencies of heavy metals were achieved with solid concentration of 6% (w/v) bioleaching treatment: Cu, 73.08%; Zn, 78.67%; Pb, 24.65%; Cd, 79.46%. The characterization results of thermogravimetric analysis (TGA) showed that the bioleached sewage sludge with a 6% (w/v) solid concentration treatment was the easiest to decompose. Pyrolytic experiments of bioleached sewage sludge were performed in a laboratory-scale fixed bed reactor. Results indicated that bioleaching treatment greatly influenced the product yields and gas composition.

Extracellular Polymeric Substances Level Determines the Sludge Dewaterability in Bioleaching Process

AbstractBioleaching treatments can significantly improve the dewaterability of sewage sludge. However, the exact mechanisms of the improvement of sludge dewaterability by bioleaching are as yet unclear. In this study, the variation of extracellular polymeric substances (EPS) content along with bound water content in sludge during bioleaching was investigated in detail. Results showed that sludge dewaterability was improved rapidly and then deteriorated slowly. The improvement of sludge dewaterability in the first 48 h of bioleaching was primarily attributable to the removal of sludge EPS, and the deterioration of sludge dewaterability in the following 144 h primarily resulted from the unexpected increase of sludge EPS amount in the latter stage of the bioleaching treatment. The Spearman correlation coefficients of EPS content and bound water content, EPS content and the specific resistance to filtration (SRF), and bound water content and SRF were 0.81, 0.83, and 0.94, respectively. Furthermore, the dewate...

Extracellular polymeric substances and bound water drastically affect bioleached sludge dewaterability at low temperature

It is well documented that bioleaching with the co-inoculation of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans can drastically enhance sludge dewaterability under ambient temperature condition, but little information on low temperature effect on bioleached sludge dewaterability is available. In this study, the optimum sludge retention time of bioleaching treatment and the mechanisms responsible for the dewaterability enhancement of bioleached sludge were studied in two bioleaching systems conducted at a low temperature of 10°C and a normal temperature of 28°C, respectively. Results showed that Acidithiobacillus bacteria involved in the bioleaching were still active at 10°C, and sludge capillary suction time (CST) decreased in the first 3 days of bioleaching. Nevertheless, the degree of sludge dewaterability enhancement by bioleaching was much lower at 10°C than that at 28°C. The only slight decreases in the sludge pH value and relative high contents of extracellular polymeric substances (EPS) and bound water at a low temperature were responsible for the relatively lower dewaterability enhancement of bioleached sludge compared to that at the normal temperature. Moreover, statistical results showed that sludge CST had significant positive correlations with the sludge pH value, and EPS and bound water contents in the optimum bioleaching process (from day 0 to day 3). Therefore, reducing medium pH, and/or removing EPS from bioleaching bacteria and bound water of bioleached sludge through forced physical–chemical approaches prior to mechanical dewatering might be a good method to greatly improve sludge dewatering at a low temperature.

Combined ultrasonic and bioleaching treatment of hospital waste incinerator bottom ash with simultaneous extraction of selected metals

The mineralogy, as well as elemental composition, of the incinerated hospital waste (HW) ashes are not well known and need to be investigated for the safe handling and disposal of such ash. A study was conducted to investigate the chemical composition, mineralogy and bioleaching of selected metals from incinerated HW bottom ash using Aspergillus niger under the combined effect of ultrasonic radiation. Different techniques were utilized to determine the elemental composition (Electron Dispersive X-ray Spectroscopy [EDX], atomic absorption spectrophotometry, inductively coupled plasma-optical emission spectroscopy, ultraviolet-visible light spectrophotometer) and mineralogy (X-ray Diffraction) of the raw sample, as well as the bioleached samples. Chemical leaching tests were performed to determine the effect of different organic acids on metals dissolution. Microbes were tested for acid production and leaching capabilities of selected metals from medical waste (MW) bottom ash. Wet chemical and EDX analyses showed that the ash was enriched with metallic elements like Na, K, Ca, Fe and Al with a concentration range of 22–115 (g/kg). Furthermore, the ash contained heavy metals such as Cu, Cr, Ni, Sn and Ti in the range of 0.51–21.74 (mg/kg). Citric and oxalic acids generated by fungi could be important leaching agents acting to dissolve these metals. Under ultrasonic treatment, metals dissolution by the acidic metabolites was at its maximum after just 9 d of leaching. The results showed that the dissolution of metals was much higher in citric and oxalic acid than with other acids. Extraction of metals from incinerated MW ash indicated that this ash may be a potential source of metals in the future.