Effect of three typical sulfide mineral flotation collectors on soil microbial activity

Insight into the mechanisms of combined toxicity of cadmium and flotation agents in luminescent bacteria: Role of micro/nano particles

Currently, risk assessment and pollution management in mines primarily focus on toxic metals, with the flotation agents being overlooked. However, the combined effects of metals and flotation agents in mines remain largely unknown. Therefore, this study aimed to evaluate the combined effects of Cd and two organic flotation agents (ethyl xanthate (EX) and diethyldithiocarbamate (DDTC)), and the associated mechanisms. The results showed that Cd + EX and Cd + DDTC exhibited synergistic toxicity. The EC50 values for luminescent bacteria were 1.6 mg/L and 1.0 mg/L at toxicity unit ratios of 0.3 and 1, respectively. The synergistic effects were closely related with the formation of Cd(EX)2 and Cd(DDTC)2 micro/nano particles, with nano-particles exhibiting higher toxicity. We observed severe cell membrane damage and cell shrinkage of the luminescent bacteria, which were probably caused by secondary harm to cells through the released CS2 during their decomposition inside cells. In addition, these particles induced toxicity by altering cellular levels of biochemical markers and the transcriptional levels of transport proteins and lipoproteins, leading to cell membrane impairment and DNA damage. This study has demonstrated that particulates formed by Cd and flotation agents contribute to the majority of the toxicity of the binary mixture. This study helps to better understand the complex ecological risk of inorganic metals and organic flotation agents in realistic mining environments.

Hydrothermal preparation of NiO/La-NaTaO3 composite photocatalyst for degradation of ammonium dibutyl dithiophosphate wastewater

The discharge of a large amount of flotation reagents wastewater can cause significant environmental pollution. In this study, NiO/La-NaTaO3 nano-photocatalyst was prepared and applied to degrade synthetic flotation reagent ammonium dibutyl dithiophosphate wastewater. Various characterization results confirmed the successful synthesis of NiO/La-NaTaO3, and UV-vis DRS analysis revealed a band gap of 3.96 eV for 4 wt% NiO/2.5% La-NaTaO3. Under UV light, the degradation rate of 20 mg 4 wt% NiO/2.5% La-NaTaO3 photocatalyst reached its optimum within 4.5 h at pH=3, exhibiting a 1.45 times improvement compared to pure NaTaO3. Radical trapping experiments and EPR results showed that ·OH and·O2- showed major contribution to the degradation. Furthermore, photocatalytic mechanisms and toxicity evolution were investigated, demonstrating the potential application of photocatalytic methods for treating flotation reagent wastewater.

Carbonaceous material prepared by pyrolysis of refinery oily sludge for removal of flotation collectors in wastewater

The carbonaceous material (CM) prepared by refinery oily sludge was proposed to remove flotation collectors, butyl xanthate (BX), and diethyldithiocarbamate (DDTC) in synthetic wastewater. The effects of the CM on removal efficiency, adsorption kinetics, and isotherms were experimentally carried out. The surface structure and composition of CM were characterized by BET isotherm, XRD, and SEM-EDS, and the concentration of BX and DDTC was tested by UV-VIS spectrometer. The adsorption behavior and removal mechanism were investigated by zeta potential, ToF-SIMS, FTIR, etc. The removal efficiencies of BX and DDTC were both more than 99%, and the maximum adsorption capacity peaked when the pH of the solution was neutral. The two collectors were heterogeneous adsorption on the surface of CM. BX, DDTC, and related metal compounds were found on the surface of carbonaceous material, confirming the existence of both physical and chemical adsorption, and physical adsorption accounted for the main mechanism. It is proved that BX and DDTC can be removed by carbonaceous material and realize the high-effective utilization of refinery oily sludge.

Preparation of a novel photocatalytic catalyst PW9@ZnO/Ag and the photocatalytic degradation of butyl xanthate under visible light

Photocatalytic technology is attracting considerable attention for the advantages of low cost and environmentally friendly properties. In this study, a novel photocatalyst PW₉@ZnO/Ag (PZA) was synthesized hydrothermally and characterized by a variety of means. The results indicated that ZnO and Ag NPs were successfully decorated and uniformly dispersed on PW₉ to form the composites. The prepared PZA was applied in the degradation of simulated butyl xanthate (BX) beneficiation wastewater both under the UV light and the xenon lamp, and a maximum degradation of 99.83% was obtained under the visible light with 10% ZnO loading, 1 g/L PZA, initial BX concentration of 20 mg/L, and pH 5.5. The PZA was recovered and reused for 5 times, and the degradation rates remained above 70%. Superoxide radical (·O₂^-) was the main active species for the photocatalytic degradation of BX. The experimental results demonstrate that PZA is a promising photocatalyst, making it a prospective strategy to overcome current challengers in the use of xanthate degradation and beneficiation wastewater treatment under visible light.

Facile synthesis and evaluation of three magnetic 1,3,5-triformylphloroglucinol based covalent organic polymers as adsorbents for high efficient extraction of phthalate esters from plastic packaged foods

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A facile synthetic route for synthesis of three magnetic Tp-based COPs adsorbents was provided.

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Magnetic COP2 showed best extraction performance for PAEs.

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The potential adsorption mechanism was systematically investigated.

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This method was suitable for high efficient extraction of hydrophobic PAEs from foods.

Three covalent organic polymers (COPs) were successfully fabricated by room-temperature solvent-free mechanochemical grinding method between 1,3,5-triformylphloroglucinol (TP) and p-phenyl enediamine (COP1), benzidine (COP2), 4, 4″-diamino-p-terphenyl (COP3), and followed by coprecipitation on the surface of Fe₃O₄ nanoparticles to form three corresponding magnetic Tp-series COPs. The fabricated magnetic COPs were evaluated and then applied for the extraction of phthalate esters from food samples before gas chromatography-tandem spectrometry analysis. Magnetic COP2 exhibited the highest extraction efficiency, which can be attributed to its larger pore size, and its strong hydrophobic and π-π interactions with phthalate esters. The method possessed good linearity (10–1000 μg·kg⁻¹), high sensitivity (0.29–2.59 µg·kg⁻¹ for LODs and 0.97–8.63 µg·kg⁻¹ for LOQs), and satisfactory recoveries (70.2–108.1%) with relative standard deviations lower than 5.2%. This method has potentials for high efficient separation/preconcentration of hydrophobic phthalate esters from foods.

Accessing Metals from Low-Grade Ores and the Environmental Impact Considerations: A Review of the Perspectives of Conventional versus Bioleaching Strategies

Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation.

Removal of Flotation Collector O-Isopropyl-N-ethylthionocarbamate from Wastewater

Flotation collector O-isopropyl N-ethylthionocarbamate (IPETC) is widely used for separation of sulfide ores. Its removal from water by several oxidation processes was studied. Photocatalytic oxidation with air in the presence of iron salts, utilizing solar irradiation or artificial UV-A light is very efficient. Oxidation leads through the formation of O-isopropyl N-ethylcarbamate and several other reaction intermediates to total decomposition of organic compound in the final stage in 1 day. Similar results were obtained with a Fenton type oxidation with hydrogen peroxide and iron salts. Treatment with sodium hypochlorite yields mainly O-isopropyl N-ethylcarbamate. The formation of this compound in wastewaters can be of concern, since simple alkyl carbamates are cancer suspect agents.

Toxic response of the freshwater green algae Chlorella pyrenoidosa to combined effect of flotation reagent butyl xanthate and nickel

Butyl Xanthate (BX) is a typical flotation reagent used to extract non-ferrous nickel ores, discharged into the surrounding environment of mining areas in large quantities. However, few studies have focused on the toxicity of combined pollution of BX and nickel (Ni) on aquatic plants, especially phytoplankton, the main producer of aquatic ecosystems. The toxicity and potential mechanism of single and combined pollution of BX and Ni at different concentrations (0-20 mg L^-1) on typical freshwater algae (Chlorella pyrenoidosa) were studied. BX slightly stimulated the growth of C. pyrenoidosa on the first day, but Ni and Ni/BX mixture significantly inhibited it during incubation. Results showed that the inhibition rate (I) of the pollutants on the growth of C. pyrenoidosa followed the order: Ni/BX mixture > Ni > BX. The 96-h 20% effective inhibitory concentrations (96h-EC₂₀) of Ni and BX on C. pyrenoidosa growth were 3.86 mg L^-1 and 19.25 mg L^-1, respectively, indicating C. pyrenoidosa was sensitive to pollutants. The content of total soluble protein (TSP) and chlorophyll a (Chl-a) changed significantly, which may be caused by the damage of pollutants to cell structures (cell membranes and chloroplasts). In addition, the I of pollutants on C. pyrenoidosa growth was related to dose, superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA). The increasement of reactive oxygen species (ROS), antioxidant enzymes (SOD and CAT), and MDA content, suggested C. pyrenoidosa suffered from oxidative stress, leading to lipid oxidation. These results will help to understand the toxicity mechanism of pollutants in typical mining areas and assess the environmental risks of pollutants to primary producers in aquatic ecosystems.

Review of Potential Microbial Effects on Flotation

Microorganisms enter the flotation process mainly from intake water and ore material. The diversity and number of microorganisms can vary significantly from mine to mine. In flotation, the conditions including oxygen levels, temperature, and nutrients from ore, intake water, and reagents are often favorable for the microbial growth. The mining industry aims to close the water loops, which is expected to result in the accumulation of microorganisms in the process waters with potential effects on flotation performance. Bioflotation, bioleaching, and bio-oxidation have been studied for decades as tools for concentrating and dissolving minerals. In contrast, there is limited scientific literature or industrial knowledge about microorganisms that naturally inhabit and prevail in minerals processing applications over a wide pH range. Microorganisms affect minerals when they selectively attach to the surfaces, produce extracellular polymeric substances (EPS) and polysaccharides, oxidize or reduce the minerals, change the pH and Eh of the process solution, and degrade organic flotation chemicals. Microorganisms contain different structural components that affect their surface chemistry, charge, and behavior in flotation, but these properties may also change via adaptation and solution conditions. Almost all studies on flotation have focused on chemical and physical parameters, and the role of naturally occurring microorganisms has remained underexplored. Advances in genomics and proteomics offer possibilities to describe not only which microorganisms are present, but also which physiological functions are being exercised. This article reviews the current knowledge of microorganisms in various mineral processes, identifies potential microbe–mineral interactions in flotation, describes the gaps in current knowledge, and concludes with the potential effects of microorganisms on flotation, especially in closed water loops.

Effects of typical flotation reagent on microbial toxicity and nickel bioavailability in soil

The combined toxicological effects of nickel (Ni) and butyl xanthate (BX), that is commonly used in flotation reagents for non-ferrous metals ore processing such as Ni, copper and lead ores, on soil microbial communities were studied by determining soil microbial activity, soil enzyme activities and Ni bioavailability. The results revealed that the exchangeable (EXC) and reducible (RED) fractions of Ni were higher in Ni/BX mixture than Ni alone, probably because BX reacts with Ni to form complexes that lead an increase in bioavailability of Ni. The presence of BX and Ni inhibited microbial activity and enzyme activities during the first 30-days. Then, from 30 days to 180 days, different trends were observed according to the condition: microbial activity was stimulated with BX alone while it was inhibited with Ni/BX mixture. This observation was supported by the fact that the inhibitory ratio (I) was higher for Ni/BX mixture than BX alone. Results showed that the sensitivity to one or both contaminants followed the order: urease (UA) > invertase (INV). EXC fraction of Ni/BX mixture were significantly correlated with UA, INV, I, peak power (P_peak) and peak time (T_peak), respectively (p < 0.01), suggesting that Ni bioavailability might explain the Ni toxicity against microbial communities under combined pollution conditions. Such observations allow us to better understand toxic effects of Ni pollution when accompanied with BX, facilitating precisely evaluation of potential risks in mining areas.

UV185+254 nm photolysis of typical thiol collectors: decomposition efficiency, mineralization and formation of sulfur byproducts

The decomposition of toxic flotation reagents upon UV_{185+254 nm} irradiation was attractive due to operational simplicity and no dosage of oxidants. In this work, the degradation of typical thiol collectors (potassium ethyl xanthate (PEX), sodium diethyl dithiocarbamate (SDD), O-isopropyl-N-ethyl thionocarbamate (IET) and dianilino dithiophoshoric acid (DDA)) was investigated by UV_{185+254 nm} photolysis. The degradation efficiencies and mineralization extents of collectors were assessed. The formation of CS₂ and H₂S byproducts was studied, and the mechanisms of collector degradation were proposed under UV_{185+254 nm} irradiation. The PEX, SDD and IET were decomposed with nearly 100% removal upon 75 min of UV_{185+254 nm} irradiation. The decomposition rate constants decreased in the order SDD > PEX > IET ≫ DDA, and the DDA was the refractory collector. After 120 min of UV_{185+254 nm} irradiation, 15-45% of carbon and 25-75% of sulfur of collectors were completely mineralized, and the mineralization extent decreased in the order PEX > SDD > IET > DDA. The percentage of gaseous sulfur (CS₂ and H₂S) ranged from 0.48 to 4.85% for four collectors, showing the fraction of emitted sulfur byproducts was small. The aqueous CS₂ concentration increased in the first 10-20 min, and was decreased to a low level of 0.05-0.1 mg l^-1 at 120 min. Two mechanisms, i.e. direct UV_{254 nm} photolysis and indirect oxidation with free radicals, were responsible for collector decomposition in the UV_{185+254 nm} photolysis.

Characterization of microbial communities of soils from gold mine tailings and identification of mercury-resistant strain

To enrich the understanding of the complex environmental system of soil and microorganisms in gold tailings, we studied the effects of environmental factors on the microbial community diversity in gold mine tailing soil in Beijing, and the strains screened from the soil with serious mercury (Hg) pollution. The results showed that microbial diversity and community composition varied among sites, and at varying depths, soil microbes were significantly affected by soil environmental factors such as lead (Pb), Hg, pH, and total organic carbon (TOC). Pb and Hg negatively affected soil microbial diversity, and less-polluted soil showed increased microbial diversities and complex community structure. Community composition analysis showed that Firmicutes, Proteobacteria and Actinobacteria were the dominant microorganisms. Moreover, Hg-resistant bacterial species isolated from soil samples were identified as Pseudomonas plecoglossicida with a high Hg tolerance efficiency. This study is important in understanding the microbial diversity and function in gold mine tailing soils and can widen the application for bioremediation process.

Microcalorimetry and enzyme activity to determine the effect of nickel and sodium butyl xanthate on soil microbial community

In non-ferrous metal tailings, combined pollution in the surrounding soil is caused by heavy metals and flotation chemicals. The combined effects of nickel (Ni) and its primary ore processing collector, sodium butyl xanthate (SBX), on soil microbial activity were investigated following the fluorescein diacetate hydrolase (FDA) and sucrase (SA) activities, and isothermal microcalorimetry during 60 days. FDA and SA activities as well as overall soil microbial activity were significantly affected by Ni, SBX and Ni/SBX mixture. The inhibition rate (I) of the growth rate constant (k) being higher with the Ni/SBX mixture than with SBX alone during the experiment. The growth rate constant (k) was positively correlated (p < 0.05 or p < 0.01) with enzyme activities (FDA and SA) indicating that k represented a valuable proxy to evaluate the toxic effect of metals and flotation reagents on soil microorganisms. Thus, microcalorimetry was a useful method to characterize soil microbial communities.

Combined effects of antimony and sodium diethyldithiocarbamate on soil microbial activity and speciation change of heavy metals. Implications for contaminated lands hazardous material pollution in nonferrous metal mining areas

The combined effects of antimony (Sb) and sodium diethyldithiocarbamate (DDTC), a common organic flotation reagent, on soil microbial activity and speciation changes of heavy metals were investigated for the first time. The results showed that the exchangeable fraction of Sb was transformed to a stable residual fraction during the incubation period, and the addition of DDTC promoted the transformation compared with single Sb pollution, probably because DDTC can react with heavy metals to form a complex. In addition, the presence of DDTC and Sb inhibited the soil microbial activity to varying degrees. The growth rate constant k of different interaction systems was in the following order on the 28th day: control group ≥ single DDTC pollution > combined pollution > single Sb pollution. A correlation analysis showed that the concentration of exchangeable Sb was the primary factor that affected the toxic reaction under combined pollution conditions, and it significantly affected the characteristics of the soil microorganisms. All the observations provide useful information for a better understanding of the toxic effects and potential risks of combined Sb and DDTC pollution in antimony mining areas.

Toxicity of nickel to soil microbial community with and without the presence of its mineral collectors-a calorimetric approach

The toxicity of nickel and three of its main collectors, sodium isopropyl xanthate (SIPX), sodium ethyl xanthate (SEX), and potassium ethyl xanthate (PEX) to soil microbial activity, was analyzed, individually and as a binary combination of nickel and each of the collectors. The investigation was performed through the microcalorimetric analysis method. For the single chemicals, all power-time curves exhibited lag, exponential, stationary, and death phases of microbial growth. Different parameters exhibited a significant adverse effect of the analyzed chemicals on soil microbial activity, with a positive relationship between the inhibitory ratio and the chemical dose (p < 0.05 or p < 0.01). A peak power reduction level of 24.23% was noted for 50 μg g^-1 soil in the case of Ni while for the mineral collectors, only 5 μg g^-1 soil and 50 μg g^-1 soil induced a peak power reduction level of over 35 and 50%, respectively, in general. The inhibitory ratio ranged in the following order: PEX > SEX > SIPX > Ni. Similar behavior was observed with the mixture toxicity whose inhibitory ratio substantially decreased (maximum decrease of 38.35%) and slightly increased (maximum increase of 15.34%), in comparison with the single toxicity of mineral collectors and nickel, respectively. The inhibitory ratio of the mixture toxicity was positively correlated (p < 0.05 or p < 0.01) with the total dose of the mixture. In general, the lesser and higher toxic effects are those of mixtures containing SIPX and PEX, respectively.

Toxic effect of two kinds of mineral collectors on soil microbial richness and activity: analysis by microcalorimetry, microbial count, and enzyme activity assay

Flotation reagents are hugely and increasingly used in mining and other industrial and economic activities from which an important part is discharged into the environment. China could be the most affected country by the resulting pollution. However, their ecotoxicological dimension is still less addressed and understood. This study aimed to analyze the toxic effect of sodium isobutyl xanthate (SIBX) and sodium isopropyl xanthate (SIPX) to soil microbial richness and activity and to make a comparison between the two compounds in regard to their effects on soil microbial and enzymes activities. Different methods, including microcalorimetry, viable cell counts, cell density, and catalase and fluorescein diacetate (FDA) hydrololase activities measurement, were applied. The two chemicals exhibited a significant inhibitory effect (P < 0.05 or P < 0.01) to all parameters, SIPX being more adverse than SIBX. As the doses of SIBX and SIPX increased from 5 to 300 μg g^-1 soil, their inhibitory ratio ranged from 4.84 to 45.16 % and from 16.13 to 69.68 %, respectively. All parameters fluctuated with the incubation time (10-day period). FDA hydrolysis was more directly affected but was relatively more resilient than catalase activity. Potential changes of those chemicals in the experimental media and complementarity between experimental techniques were justified.