Zinc Mine Tailings Research Articles

Discussion of ‘Strength Evaluation of Expansive Soil Stabilized with Lead–Zinc Mine Tailings and Cement: An Artificial Intelligence Approach’ [DOI: 10.1007/s42947-024–00450-y

Discussion of ‘Strength Evaluation of Expansive Soil Stabilized with Lead–Zinc Mine Tailings and Cement: An Artificial Intelligence Approach’ [DOI: 10.1007/s42947-024–00450-y

Strength Evaluation of Expansive Soil Stabilized with Lead–Zinc Mine Tailings and Cement: An Artificial Intelligence Approach

Strength Evaluation of Expansive Soil Stabilized with Lead–Zinc Mine Tailings and Cement: An Artificial Intelligence Approach

Mineralogical Characterization of the Grot Lead and Zinc Mine Tailings from Aspects of Their Further Use as Raw Material

The possibility of using waste tailings produced by flotation in the lead and zinc mine of Grot, Serbia as a potential source of secondary mineral raw materials was examined. The aim of the research was primarily to carry out a detailed characterization in order to determine the dominant minerals, and, for the first time, to trace the changes occurring in the unit cells of the minerals present in that deposit. There was also a need to determine the exact proportions of the present mineral phases for their further application and utilization as natural resources in environmental protection. Samples were taken from three different sections of tailings: the crest of dam (JKB), outlet pipe of the flotation facility (JOF) and hydrocyclone overflow (JHC). Granulometric separation was performed to facilitate the extraction of certain minerals from waste. The results showed that all samples mainly contained quartz, clinochlore, calcite, albite, pyrite and biotite, but their ratios in each sample varied significantly. After characterization, samples were separated into different fractions and their mineralogical compositions were determined. Depending on the fraction, the mineralogical compositions also changed. Mineralogy and geochemical analysis indicate that waste tailings can be used as a secondary mineral raw materials source applicable in various industries.

Root-associated bacterial microbiome shaped by root selective effects benefits phytostabilization by Athyrium wardii (Hook.)

The root-associated microbiome assembly substantially promotes (hyper)accumulator plant growth and metal accumulation and is influenced by multiple factors, especially host species and environmental stress. Athyrium wardii (Hook.) is a phytostabilizer that grows in lead (Pb)-zinc (Zn) mine tailings and shows high root Pb accumulation. However, there remains little information on the assembly of the root-associated microbiome of A. wardii and its role in phytostabilization. A field study investigated the structural and functional variation in the root-associated bacterial microbiome of Athyrium wardii (Hook.) exposed to different levels of contamination in Pb-Zn mine tailings. The root compartment dominated the variation in the root-associated bacterial microbiome but the levels of contaminants showed less impact. Bacterial co-occurrence was enhanced in the rhizosphere soil and rhizoplane but tended to be much simpler in the endosphere in terms of network complexity and connectivity. This indicates that the microbial community assembly of A. wardii was non-random and shaped by root selective effects. Proteobacteria, Chloroflexi, Actinobacteria, Cyanobacteria, and Acidobacteriota were generally the dominant bacterial phyla. The genera Crossiella and Bradyrhizobium were enriched in the rhizosphere and cyanobacterial genera were enriched in the endosphere, demonstrating substantial advantages to plant survival and adaptation in the harsh mine environment. Functional categories involved in amino acid and carbohydrate metabolism were abundant in the rhizosphere soil, thus contributing to metal solubility and bioavailability in the rhizosphere. Membrane transporters, especially ATP-binding cassette transporters, were enriched in the endosphere, indicating a potential role in metal tolerance and transportation in A. wardii. The study shows substantial variation in the structure and function of microbiomes colonizing different compartments, with the rhizosphere and endophytic microbiota potentially involved in plant metal tolerance and accumulation during phytostabilization.

Environmental contamination characteristics of heavy metals from abandoned lead–zinc mine tailings in China

China holds large-scale lead–zinc mineral resources; however, mining activities often cause severe contamination by heavy metals. This study systemically assessed contamination by eight heavy metals (Cu, Zn, Cd, Pb, Cr, Hg, Ni, and As) in mine tailings, soil, and groundwater from 27 contaminated sites across China. Regarding mine tailings, 1% of the mine tailing samples were hazardous waste and 20% were class II non-hazardous waste. Regarding soil, Zn and Pb showed the highest mean concentrations, at 5574.67 mg/kg and 2034.88 mg/kg, respectively. The indexes of geo-accumulation (Igeo) of eight heavy metals ranged from −3.62 to 7.67, while Zn, Pb, and Cd showed the highest environmental risk levels as the priority pollutants. The contamination levels of these heavy metals in groundwater were generally in the order of Zn>As>Pb>Ni>Cd>Cu>Hg>Cr. In this study, 20% of the soil and 10% of the groundwater samples exceeded the corresponding quality limits. The content of heavy metals in soil, groundwater, and mine tailing were positively correlated, demonstrating the main pollution source and transport paths. The pollution levels of heavy metals in soil and groundwater were listed in the foremost and moderate positions compared with similar sites from other countries, respectively. These results may help determine the pollution levels of lead–zinc mining regions and direct the remediation activities of target sites to support the environmental management of abandoned mining and tailing waste in China.

Mechanical activation of lead–zinc mine tailings as a substitution for cement in concrete construction

Use of mine tailings as a replacement for cement in concrete construction is a highly efficient method to reduce the environmental pollution of tailings’ accumulation including toxic elements, acid mine drainage, and dust emission. Thus, safe management and accurate reuse of tailings is necessary. In this research, lead–zinc mine tailings (LZTs) were used and their reactivity were improved through mechanical activation. The compressive strength, mercury intrusion porosimetry (MIP), and toxicity characteristic leaching procedure (TCLP) tests were performed on the concrete samples. The TCLP test revealed that an increase in curing days led to a significant reduction in heavy metal leaching rate (cobalt, zinc, lead, nickel, copper, arsenic, cadmium and chromium) to a permissible limit. This indicates that the application of LZTs in concrete construction would lessen environmental concerns. The MIP test indicated that mercury intrusion volume in the activated sample with 20 % cement-replacement (TA20) was lower than that of the raw sample with 20 % cement-replacement (TR20) and control (C100) samples. The results from X-ray diffraction (XRD) analysis showed that upon activating and increasing the curing time, the hatrurite converted to scawtite in samples containing activated tailings. The compressive strength results after 28 and 90 curing days revealed a rise in the strength from 16.9 MPa to 19.8 MPa for concrete samples TR20. However, upon prolonging the curing time from 28 up to 90 days, the compressive strength of the concrete samples TA20 grew from 28.35 MPa to 45.5 MPa. This indicates that the mechanical activation enhanced the hydration process and the cohesion of samples. The results of scanning electron microscopy (SEM) revealed that hydration products were also observed in concrete samples containing activated tailings. Overall, the results showed that mechanically activated LZTs, up to 40 % (by weight), can be a suitable substitute for cement in concrete production.

Carbonate mineral controls the transport of Cd from tailings to surrounding soils: An example from Cd-rich Niujiaotang Zn mine in Guizhou Province, Southwest China

Heavy metal pollution derived from the oxidation of sulfides in Pb-Zn mine tailings has been a common public concern. Although the oxidative dissolution of sphalerite will release cadmium into the soil environment, it is still unclear whether other minerals contain a large amount of cadmium and how much these minerals contribute to the surrounding environmental media. In this paper, XRD, particle size analyzer, SEM-EDS and improved BCR sequential extraction method were used to analyze cadmium rich zinc mine tailing and adjacent farmland soil in Duyun, Guizhou Province. The results show that the average contents of Pb, Zn, and Cd in tailing are 214 ± 71 mg/kg, 2668 ± 773 mg/kg, and 37.5 ± 9.97 mg/kg respectively. While in the surrounding soil, they were 519 ± 280 mg/kg, 3,779 ± 2614 mg/kg, and 30.8 ± 14.4 mg/kg respectively. The mineralogical composition of tailing is mainly dolomite and less pyrite. Cadmium in tailing is mainly in weak acid extractable state, indicating that cadmium mainly exists in dolomite of tailing. Pyrite in tailing generates acid through oxidation, which accelerates the dissolution of dolomite, thus releasing Cd from minerals and migrating to surrounding farmland, resulting in soil cadmium pollution. This study reveals an important process that has been neglected. Carbonate minerals play an important role in the migration of cadmium in the tailing of the Mississippi Valley-type (MVT) lead-zinc mine and the soils affected by the tailing.

Preparation of self-foamed glass ceramics based on the cooperative treatment of various solid wastes: Characterization of structure-properties and analysis of self-foaming behavior

Utilization of solid waste can be a preferable waste management solution. In this study, a type of self-foamed glass ceramic material was prepared using lead zinc mine tailings, red mud, and silica sand tailings through in-situ decomposition foaming. The effect of silica sand tailings content on the pore morphology, microstructure, and basic performances of the prepared specimen was analyzed. Meanwhile, the differences in the pore morphology and self-foaming behavior of the foamed glass ceramics were discussed. The obtained results indicated that the addition of silica sand tailings facilitated the formation of the glass phase in samples, and the composition, content, and viscosity of the glass phase could be changed by adjusting the content of silica sand tailings, resulting in a uniform distribution of the formed pores. Owing to their well-distributed pore structure, foamed glass ceramics exhibit excellent comprehensive properties (light weight and high strength), making them a potential non-load-bearing material. In this study, the comprehensive properties of the sample prepared with 40 wt% silica sand tailings were determined to be the best: exhibiting the lowest bulk density (0.63 g/cm3), highest porosity (72.6%), and an applicable mechanical strength (9.7 MPa). This study utilized three solid wastes through a reasonable combination based on their chemical composition, and proposed a novel technique for the preparation of self-foaming glass ceramics via the cooperative treatment of various wastes.

The bio-immobilization of Pb(II) induced by the Chlorella–montmorillonite composite in the Ca(II) environment

The clay–microbial consortium is ubiquitous in the soil near the mining area and plays an important role in the transport of heavy metals. In this study, Chlorella sorokiniana FK was separated from lead–zinc mine tailings. The montmorillonite–Chlorella sorokiniana FK system as a typical case was applied to study Pb(II) biomineralization in the presence of usually co-existent Ca(II) and further reduce the migration and transformation of Pb(II) in the Ca(II) environment. Chlorella sorokiniana FK showed good resistance to Pb(II), and the addition of montmorillonite provided a more stable pH environment, which is conducive to the stability of Pb(II)-bearing bio-minerals. Montmorillonite created a low-biotoxicity environment in the overall process, especially less Pb(II) bio-adsorption capacity of individual Chlorella to protect the process of mineralization effectively. Batch experiment results also demonstrated that montmorillonite as the formation site of bio-minerals results in dispersed minerals on the surface of Chlorella and Chlorella–MMT composite, which is beneficial to the survival of Chlorella. Moreover, Pb(II)-bearing phosphate minerals tended to form in the Ca(II) environment rather than without Ca(II). This study demonstrated the mechanism of Pb(II) immobilization induced by Chlorella in the Ca(II) environment, further presenting a green, sustainable, and effective strategy for Pb(II) bio-immobilization combining clay minerals and microorganisms.

Microstructural and compaction characteristics of tropical black clay soil subgrade modified with lead-zinc mine tailings

Lead–Zinc Mine tailings (LZMT) are wastes generated after the extraction of lead and zinc from mined mineral ore, whose disposal mechanism is gradually becoming environmentally unfriendly. For effective recycling of LZMT, this present study utilized a combination of LZMT and Portland limestone cement (PLC) to improve the compaction and microstructural characteristics of tropical black clay soil (TBCS) for use in pavement design and construction. The LZMT and PLC were added to the expansive soil in varying proportions with mix ratios generated from Taguchi orthogonal array. The result obtained for the compaction characteristics showed that the maximum dry density (MDD) increased significantly when a combination of 20% LMZT and 4% PLC were blended with the expansive soil. The increase in the MDD was attributed to the formation of cementitious compounds. In addition, the optimum mix ratio obtained from the unconfined compressive strength of the TBCS, was used for the evaluation of the pore structure characteristics which included porosity, tortuosity and permeability. The result obtained from the analysis that was implemented with a combination of fractal geometry and Bradley and Roth adaptive thresholding image segmentation technique, indicates the possibility of a slight reduction in the strength properties of the modified soil due to its high level of porosity. Also, the permeability and tortuosity values obtained from the present study suggest a slight increase in the permeability of the modified soil-additive mixtures which may not be unconnected to the occurrence of pozzolanic reaction that resulted in the agglomeration and flocculation of the LZMT-PLC modified TBCS. Furthermore, microstructural analysis was executed on the modified TBCS and LZMT using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The result from the FTIR analysis indicates the pozzolanic character of LZMT in the presence of Si–O and Al–O tension bond with the bonds around 1000 cm−1 wavenumber, while the SEM analysis reveals the formation of a cementitious compound in the modified expansive soil-LZMT-PLC mixture.

Bradyrhizobium sp. sv. retamae nodulates Retama monosperma grown in a lead and zinc mine tailings in Eastern Morocco

The aim of this work was to characterize and identify some bacteria isolated from the root nodules of Retama monosperma grown in Sidi Boubker lead and zinc mine tailings. Very few root nodules were obtained on the root nodules of R. monosperma grown in these soils. The three bacteria isolated from the root nodules were tolerant in vitro to different concentrations of heavy metals, including lead and zinc. The rep-PCR experiments showed that the three isolates have different molecular fingerprints and were considered as three different strains. The analysis of their 16S rRNA gene sequences proved their affiliation to the genus Bradyrhizobium. The analysis and phylogeny of the housekeeping genes atpD, glnII, gyrB, recA, and rpoB confirmed that the closest species was B. valentinum with similarity percentages of 95.61 to 95.82%. The three isolates recovered from the root nodules were slow-growing rhizobia capable to renodulate their original host plant in the presence of Pb-acetate. They were able to nodulate R. sphaerocarpa and Lupinus luteus also but not Glycine max or Phaseolus vulgaris. The phylogeny of the nodA and nodC nodulation genes as well as the nifH gene of the three strains showed that they belong to the symbiovar retamae of the genus Bradyrhizobium. The three strains isolated could be considered for use as inoculum for Retama plants before use in phytoremediation experiments.

Identification of the endosymbionts from Sulla spinosissima growing in a lead mine tailings in Eastern Morocco as Mesorhizobium camelthorni sv. aridi.

To identify the bacteria nodulating Sulla spinosissima growing profusely in a lead and zinc mine tailings in Eastern Morocco. In all, 32 rhizobial cultures, isolated from root nodules of S. spinosissima growing in soils of the mining site, were tolerant to different heavy metals. The ERIC-polymerase chain reaction (PCR) fingerprinting analysis clustered the isolates into seven different groups, and the analysis of the 16S rRNA sequences of four selected representative strains, showed they were related to different species of the genus Mesorhizobium. The atpD, glnII and recA housekeeping genes analysis confirmed the affiliation of the four representative strains to Mesorhizobium camelthorni CCNWXJ40-4T , with similarity percentages varying from 96·30 to 98·30%. The sequences of the nifH gene had 97·33-97·78% similarities with that of M. camelthorni CCNWXJ40-4T ; however, the nodC phylogeny of the four strains diverged from the type and other reference strains of M. camelthorni and formed a separated cluster. The four strains nodulate also Astragalus gombiformis and A. armatus but did not nodulate A. boeticus, Vachellia gummifera, Prosopis chilensis, Cicer arietinum, Lens culinaris, Medicago truncatula, Lupinus luteus or Phaseolus vulgaris. Based on similarities of the nodC symbiotic gene and differences in the host range, the strains isolated from S. spinosissima growing in soils of the Sidi Boubker mining site may form a different symbiovar within Mesorhizobium for which the name aridi is proposed. In this work, we show that strains of M. camelthorni species nodulating S. spinosissima in the arid area of Eastern Morocco constitute a distinct phylogenetic clade of nodulation genes; we named symbiovar aridi, which encompasses also mesorhizobia from other Mediterranean desert legumes.

Iron recovery from zinc mine tailings by magnetic separation followed by carbothermal reduction of self‐reducing briquettes

AbstractThe volume of tailings produced by the extractive industry has been increasing due to the processing of the low‐grade ore. This issue can cause environmental accidents and require significant investment to control the disposal of tailings. Therefore, this study aims to recover iron from zinc mine tailings by wet magnetic separation followed by the carbothermal reduction of self‐reducing briquettes. Two magnetic separation routes were investigated to concentrate iron. Zinc mine tailings were processed by route I, in a rougher stage followed by a scavenger stage; and route II, in a rougher stage followed by a cleaner stage. The carbothermal reductions were performed using self‐reducing briquettes composed of Fe concentrate from the route with high Fe content and charcoal. The products were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM‐EDS), x‐ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP‐OES), and volumetric chemical analysis. Magnetic separation route II provided the highest‐grade Fe concentrate, 52% Fe, while route I provided 33% Fe. In the carbothermal reductions, a metallization degree of 98% in the Fe concentrate briquette, 97% in the briquette with a 10% replacement of its raw material by Fe concentrate, and 99% in the hematite briquette was reached. The replacement of raw material by Fe concentrate showed no significant change in Fe recovery. Considering the whole process, magnetic separation and carbothermal reduction, the recovery of Fe from the zinc mine tailings was 67%. Therefore, the process route suggested in this study will not only reduce tailings disposal and consequently the risk of environmental accidents, but it will also provide profitable raw material for the steel industry.

Promoting the performance of one-part alkali-activated slag using fine lead-zinc mine tailings

The feasibility of using fine lead–zinc mine tailings to improve the performance of one-part alkali-activated slag (AAS) with low alkali dosage (1.5 Na2O wt.%) is investigated. The compressive strength of one-part AAS increases with the increase of fine tailings at the early age (≤7 d), and then slightly decreases after 28 d of curing. Two distinguished reaction stages with two dormant periods are identified in all samples, regardless of the content of fine tailings. The incorporation of fine tailings accelerates the second reaction stage, but has little effect on the first reaction stage. The pH value of the pore solution in all samples increases with the reaction time (≤14 d), and those with a high content of fine tailings give relatively high alkalinity values at all curing ages. The incorporation of fine lead–zinc mine tailings enhances the compressive strength of one-part AAS, which is mainly associated with its roles of improving the pH value in pore solutions and accelerating the reaction of binders.

Effects of peat on plant growth and lead and zinc phytostabilization from lead-zinc mine tailing in southern China: Screening plant species resisting and accumulating metals

In order to investigate the toxicity-resistance of eighteen Chinese native plants in lead (Pb)-zinc (Zn) mine tailings, we categorized their resistance to Pb and Zn, and tested their potential for phytoremediation effectiveness of Pb and Zn. Fourteen woody plant species belonging to 12 families, and 4 herbaceous species belonging to 4 families, were grown in pots with mixtures of 100% tailing +0% peat (CK), 90% tailing +10% peat (A1), and 80% tailing + 20% peat (A2), respectively. Plant height and biomass, chlorophyll content, and Pb and Zn contents of non-rhizosphere spoil mixtures and plant tissues were measured. Fifteen of the plants grew in all three spoil mixtures. Both A1 and A2 had higher plant height and biomass increment and chlorophyll contents than CK. The content of Pb and Zn in plant shoots and roots was CK > A1 > A2. The value of BCF less than 0.1, compared to 1, was a more precise classification basis for plants excluding metals. Screening for Pb and Zn resistant plants and their bioremediation potential produced the following candidate species: Sapium sebiferum, Salix matsudana, Hibiscus cannabinus, Corchorus capsularis, Ricinus communis, and Populus nigra. These species were highly Pb and Zn tolerant species, with notable growth characteristics and capacities to bioaccumulate Pb and Zn from the mine tailings. Compared to CK, the removal of Pb and Zn from non-rhizosphere spoil increased by an average of 9.64% and 9.6%, respectively in A1, but decreased in A2. The results indicated candidate species and 10% peat addition in the tailing were significant in phytoremediation of Pb and Zn regarding environmental safety.

Spatial distribution and environmental implications of heavy metals in typical lead (Pb)-zinc (Zn) mine tailings impoundments in Guangdong Province, South China.

Heavy metal pollution from mining tailings has become a serious concern in China. Here, we quantitatively evaluated the accumulation status and environmental risk of the tailings impoundments located in a typical Pb-Zn mining area in Guangdong Province, South China. The distributional characteristics of the heavy metals in the tailings impoundment area were analyzed. The results showed that the spatial distributions of the heavy metals contained in the tailings were dependent on the geochemical characteristics of the mine tailings rather than on their diversified profile depths. Furthermore, the risk assessment of the heavy metal pollution in the soils surrounding the tailings impoundment showed that the comprehensive Nemerow pollution index (NPI) of the tested surface soil samples was higher than 3.0; thus, these values were much greater than those of the deep soil. Meanwhile, multivariate statistical analysis revealed that the heavy metals contained in the surrounding soils, such as Pb, Zn, Cu, Cd, As, and Tl, experienced similar geochemical processes. The analysis of drainage water samples indicated that surface runoff from the tailings impoundment was the main route for the migration of heavy metals. Moreover, the alkaline substances would be consumed by the acid that is continuously generated in the tailings pond, and this increases the risk of heavy metals migrating from the tailings impoundment area. Lastly, resource analysis and process mineralogy analysis showed that the tailings had a high recovery value, and the recovery of tailings would completely eliminate the environmental risks posed by the tailings.

Acid production potentials of massive sulfide minerals and lead-zinc mine tailings: a medium-term study.

Weathering of sulfide minerals is a principal source of acid generation. To determine acid-forming potentials of sulfide-bearing materials, two basic approaches named static and kinetic tests are available. Static tests are short-term, and easily undertaken within a few days and in a laboratory. In contrast, kinetic tests are long-term procedures and mostly carried out on site. In this study, experiments were conducted over a medium-term period of 2 months, not as short as static tests and also not as long as kinetic tests. As a result, pH and electrical conductivity oscillations as a function of time, acid-forming potentials and elemental contents of synthetically prepared rainwater leachates of massive sulfides and sulfide-bearing lead-zinc tailings from abandoned and currently used deposition areas have been determined. Although the lowest final pH of 2.70 was obtained in massive pyrite leachate, massive chalcopyrite leachate showed the highest titrable acidity of 1.764 g H2SO4/L. On the other hand, a composite of currently deposited mine tailings showed no acidic characteristic with a final pH of 7.77. The composite abandoned mine tailing leachate had a final pH of 6.70, close to the final pH of massive galena and sphalerite leachates, and produced a slight titrable acidity of 0.130 g H2SO4/L.

Heavy metals leaching in bricks made from lead and zinc mine tailings with varied chemical components

The stabilization/solidification approach has received considerable attentions for the disposal of hazardous metal-bearing mine tailings. A poor understanding of the immobilization mechanism of heavy metals in final products always restricts its practical applications. We reported that, the stabilization of toxic heavy metals (Zn, Pb, Cd and Cu) in bricks made from the lead and zinc mine tailings (LZMT) was highly dependent on the relative contents of SiO2, Al2O3, Fe2O3, CaO and MgO in LZMT. As the (SiO2+Al2O3)/(Fe2O3+CaO+MgO) ratios (SA/FCM ratios) increased, the CPb, CCd, or CCu in leachates slightly decreased first and then increased. Much differently, CZn firstly increased and then decreased, having highest CZn (3.92mg/L at 30th day) at the SA/FCM ratios of 0.80. Compared with CZn and CPb, a much small CCd and CCu can be found. Notably, the CZn and CPb are also impacted by the change of SiO2:Al2O3 ratios (and Fe2O3:CaO:MgO ratios as well). The CPb decreased as the SiO2:Al2O3 ratios increased from 1:0.046 to 1:1.354, while the CZn reached a highest value at SiO2:Al2O3 ratio of 1:0.084. The XRD analysis suggests that, the Al and Si can interact with Pb to form PbAl2Si2O8, which facilitates the immobilization of Pb2+. Excessive amount of SiO2 and Al2O3 bring the difficulties to forming stabile skeletons, resulting in the leaching of Pb readily. As for Zn, higher CZn is generally owing to the occurrence of acid-soluble Zn2SiO4 in bricks. The stabilization of Zn was achieved once Al3+ was introduced as host to be substituted by Zn2+ in the aluminate or aluminosilicate matrix. The findings could enrich the mechanistic understanding and pathway of heavy metals immobilization in eco-environmental products from LZMT.

Low-cost and environment-friendly ceramic foams made from lead–zinc mine tailings and red mud: Foaming mechanism, physical, mechanical and chemical properties

Ceramic foams were prepared by powder technology using lead–zinc mine tailings, red mud and silica sand as the major component, Na2B4O7 as the flux agent. The influence of the sintering temperature on the phase evolution, pore morphology, bulk density, water absorption, porosity, thermal conductivity, mechanical properties and chemical stability was studied. The experimental results showed that a process of desulfurization was observed. With increasing sintering temperature, the bulk density decreased while the porosity and the water absorption both increased. The SEM images showed that larger pores and smaller pores were formed at high temperature. These differences may be caused by the different foaming mechanisms. The thermal conductivity of samples decreased and later increased and the bending strength decreased with increasing the sintering temperature. Based on these results, the sample sintered at 970°C had a bulk density of 0.56g/cm3, a porosity of 76.2%, a bending strength of 5.3MPa and a thermal conductivity of 0.21W/(mK). Furthermore, because of its high porosity and lower thermal conductivity, the ceramic foams prepared in this work would be suitable for thermal insulation in the building industry.

Biomineralization of Pb(II) into Pb-hydroxyapatite induced by Bacillus cereus 12-2 isolated from Lead–Zinc mine tailings

The remediation of Pb(II) through biomineralization is rergarded as a promising technique as well as an interesting phenomenon for transforming heavy metals from mobile species into very stable minerals in the environment. Studies are well needed for in-depth understanding the mechanism of Pb(II) immobilized by bacteria. In the present study, we investigated the uptake and biomineralization of Pb(II) using Bacillus cereus 12-2 isolated from lead–zinc mine tailings. The maximum Pb(II) uptake capacity of B. cereus 12-2 was 340mg/g at pH 3.0. Zeta potential analyses and selective passivation experiments demonstrated that electrostatic attraction was the main force driving the uptake of Pb(II), while the carboxyl, amide and phosphate functional groups of the bacteria provided the binding sites for immobilizing Pb(II). XRD and TEM investigation revealed that the Pb(II) loaded on bacteria could be stepwise transformed into rod-shaped Ca2.5Pb7.5(OH)2(PO4)6 nanocrystal. Combined with protein denaturalization experiments, we proposed that the biomineralization of Pb(II) possibly consisted of two steps: (1) Rapid biosorption of Pb(II) on B. cereus 12-2 through the synergy of electrostatic attraction, ionic exchange and chelating activity of functional groups; (2) enzyme-mediated mineral transformation from amorphous precipitate to rod-shaped crystalline minerals happening gradually inside the bacteria.