This work examines the rates of bioremediation during a landfarming process. A field study was performed using three types of soil, which were contaminated with two different hydrocarbon concentrations: 20,000 and 50,000 ppm of total petroleum hydrocarbons (TPH). They were subjected to landfarming under the action of different treatments, based on the provision of irrigation, aeration by rototilling, fertilizer, and surfactant. The biodegradation of TPH, considering concentration and families of hydrocarbon compounds (including polycyclic aromatic hydrocarbons, PAHs), was precisely measured for a period of 486 days. The results show how biodegradation rates depend on soil texture, initial contamination level, and type of amendment. Thus, the combination of fertilizer, irrigation, and aeration was the best treatment for treating the soil contaminated with 20,000 ppm of TPH (TPH final concentrations were reduced to a range of 49 to 62% depending on the soil texture). In the case of parcels contaminated with 50,000 ppm of TPH, the most effective treatment combined the supply of fertilizer, surfactant, irrigation, and aeration (TPH final concentrations were reduced to a range of 47 to 63%, depending on the soil texture). The best biodegradation results are obtained for soils with coarser textures and using the treatment with fertilizer, irrigation, and aeration. In addition, the application of surfactant did not imply a significant improvement in the level of biodegradation of hydrocarbons in soil contaminated with 20,000 ppm of TPH, whereas in soils contaminated with 50,000 ppm of TPH, it played a leading role.
Developing urbanization, water shortage, watercourse pollution, and demands for more food due to population growth require a more efficient water irrigation and fertilizer application. Retaining nutrients and water in agricultural soils brings about higher crop yields and prevents pollution of water courses. Among different solutions, zeolites, which are environmental friendly, ubiquitous, and inexpensive, have been extensively employed in agricultural activities. These minerals are considered as soil conditioners to improve soil physical and chemical properties including infiltration rate, saturated hydraulic conductivity (Ks), water holding capacity (WHC), and cation exchange capacity (CEC). Natural and surface-modified zeolites can efficiently hold water and nutrients including ammonium (NH4+), nitrate (NO3?) and phosphate (PO43?), potassium (K+), and sulfate (SO42?) in their unique porous structures. Their application as slow-release fertilizers (SRFs) are reported as well. Therefore, zeolite application can improve both water use efficiency (WUE) and nutrient use efficiency (NUE) in agricultural activities and consequently can reduce the potential of surface and groundwater pollution. This review paper summarizes findings in the literature about the impact of zeolite applications on water and nutrient retention in the agriculture. Furthermore, it explores benefits and drawbacks of zeolite applications in this regard.
In this study, the optimum conditions for the ammonia removal from aqueous solution by microwave-assisted air stripping have been investigated at pH 11. Ammonia solution with five different initial ammonia concentrations was prepared synthetically. The Taguchi method was applied to optimize the ammonia removal conditions. Initial ammonia concentration, air flow rate, temperature, stirring speed, microwave radiation power, and radiation time were defined as the optimization parameters. Experiments were carried out at five different levels for each operational parameter. The results of the experiments revealed that 1800 ppm of initial ammonia concentration, 7.5 L min?1 of air flow rate, 60 °C of temperature, 500 rpm of stirring speed, and 500 W of microwave radiation power for 180 min. of microwave radiation time are optimum conditions for complete ammonia removal. In addition to present experimental data, the optimum operational conditions predicted by the balanced characteristics of orthogonal array were confirmed experimentally. Finally, the effect of optimization parameters was discussed in detail.
Although dilution of lake water has been used for improvement of water quality and algal blooms control, it has not necessarily succeeded to suppress the blooms. We hypothesized that the disappearance of algal blooms by dilution could be explained by flow regime, nutrient concentrations, and their interaction. This study investigated the effects of daily renewal rate (d), nitrogen (N) and phosphorus (P) concentration, and their interaction on the domination between Microcystis aeruginosa and Cyclotella sp. through a monoxenic culture experiment. The simulation model as functions of the N:P mass ratio and dilution rate (D) (calculated from d) was constructed, and the dominant characteristics of both species were predicted based on the model using parameters obtained in a monoculture experiment and our previous study. Results of monoxenic culture experiment revealed that M. aeruginosa dominated in all conditions (d = 5 or 15%; N = 1.0 or 2.5 or 5.0 mg-N L?1; P = 0.1 or 0.5 mg-P L?1) and the predicted cell densities were substantially correspondent to experimental data. Under various N:P ratios and D values, characteristics of domination for each species were predicted, indicating that Cyclotella sp. tended to be dominant under high P concentrations (P ≥ 0.36 mg-P L?1) when the N:P ratio was less than 7.0, and M. aeruginosa could not form algal blooms at the N:P ratio ≤ 7.0 (N ≤ 0.7 mg-N L?1). It was also suggested that the dilution rate leading to the Cyclotella sp. domination required 0.20 day?1 or higher regardless of the N:P ratios.
Graphical Abstract? M. aeruginosa and Cyclotella sp. could be a superior competitor in nutrient-limited and nutrient-rich conditions, respectively. ? The simulation model in this study indicated that the predicted cell density and nutrient concentration were substantially correspondent to experimental data. ? The model predicted that Cyclotella sp. tended to be dominant at the P ≥ 0.36 mg-P L?1 when the N:P ratio was less than 7.0, and M. aeruginosa could not form algal blooms at the N:P ratio ≤ 7.0 (N ≤ 0.7 mg-N L?1).
This study presents a combination of dispersive liquid-liquid-solidified floating organic drop microextraction (DLLSFODM) and slotted quartz tube (SQT) with conventional flame atomic absorption spectrometry (FAAS) to improve the sensitivity for cadmium determination. A ligand namely 2-(4-methylphenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline which has not been used in trace analyte determination was used to form a cadmium complex. Stepwise optimization of parameters affecting complex formation (pH, ligand, and buffer solution) and extraction (extraction and dispersive solvents, salt effect and mixing) was done to maximize cadmium absorbance. The slotted quartz tube was fitted onto the flame burner and optimized to increase residence time of atoms in the flame. Instrumental parameters such as sample and fuel flow rate were also optimized to further enhance the absorbance signal for cadmium. Using optimal parameters and values, the limits of detection and quantification were determined to be 0.81 and 2.69 μg L?1, respectively. Low percent relative standard deviations (<?6.0%) indicated good precision for both extraction and instrumental measurements. Recovery tests were used to determine the accuracy of the method and the recovery results obtained were between 88 and 113%.
Mercury (Hg) is an environmental pollutant which is detrimental to the health of living beings due to the toxicity in its all oxidation states. To control mercury pollution development of low cost, efficient and highly sensitive prototype mercury sensor remains a challenge. In the present work, we have proposed a low-cost prototype device based on silver nanoparticle-impregnated poly(vinyle alcohol) (PVA-Ag-NPs) nanocomposite thin film for mercury detection. The thin film, fabricated through a facile protocol, is shown to be a fast, efficient, and selective sensor for Hg2+ in aqueous medium with a detection limit of 10 ppb. We have utilized the aggregation and amalgamation of Ag-NPs with Hg2+ to develop the low-cost, highly efficient and feasible prototype mercury sensor. In the presence of Hg2+, the yellowish thin film turned into colourless due to the loss of intense surface plasmon resonance (SPR) absorption band of the silver nanoparticles (Ag-NPs) through aggregation and amalgamation with mercury. The developed sensor has high selectivity for Hg2+ ions over a wide range of other competing heavy metal ions, generally present in water of natural sources. The sensor response is found to be linear over the Hg2+ ion concentration regime from 10 ppb to 5 ppm. The developed sensor has shown to determine a trace Hg2+ ions in real water samples. Finally, using the proposed technique, we have developed a simple and inexpensive prototype device for monitoring in field environmental mercury pollution.
Ozonation is an efficient process for the primary degradation of most substrates but not for their mineralisation. In this work, the ozonation enhanced with the addition of H2O2 was studied for two substrates with very different oxidation resistances: the dye rhodamine 6G (R6G) and the surfactant linear alkylbenzene sulfonate (LAS). With O3 only, the primary degradation of R6G was completed in less than 10 min but its TOC removal only reached 45% in 1 h. By adding H2O2, TOC removal was increased to 70% with a molar ratio (mol H2O2/mol substrate) of 10. The analysis of pH decrease served to define the specific basicity loss (SBL). The optimum conditions for the R6G mineralisation were found to be associated with a SBL value between 1 and 10 ((min/g)/L)?1, through an adequate addition of H2O2. Moreover, in the case of LAS, the addition of H2O2 for a greater efficiency should occur after the foaming period, above all formed at acid pH. LAS degradation was also considerably improved, and the optimum for primary degradation achieved in 10 min with a TOC removal of over 65% with a molar ratio (mol H2O2/mol substrate) of 20.
Agricultural practises impact soil properties and N transformation rate, and have a greater effect on N2O production pathways in agricultural soils compared with natural woodland soils. However, whether agricultural land use affects N2O production pathways in acidic soils in subtropical regions remains unknown.
Materials and methods
In this study, we collected natural woodland soil (WD) and three types of agricultural soils, namely upland agricultural (UA), tea plantation (TP) and bamboo plantation (BP) soils. We performed paired 15N-tracing experiment to investigate the effects of land use types on N2O production pathways in acidic soils in subtropical regions in China.
Results and discussion
The results revealed that heterotrophic nitrification is the dominant pathway of N2O production in WD, accounting for 44.6 % of N2O emissions, whereas heterotrophic nitrification contributed less than 2.7 % in all three agricultural soils, due to a lower organic C content and soil C/N ratio. In contrast, denitrification dominated N2O production in agricultural soils, accounting for 54.5, 72.8 and 77.1 % in UA, TP and BP, respectively. Nitrate (NO3?) predominantly affected the contribution from denitrification in soils under different land use types. Autotrophic nitrification increased after the conversion of woodland to agricultural lands, peaking at 42.8 % in UA compared with only 21.5 % in WD, and was positively correlated with soil pH. Our data suggest that pH plays a great role in controlling N2O emissions through autotrophic nitrification following conversion of woodland to agricultural lands.
Conclusions
Our results demonstrate the variability in N2O production pathways in soils of different land use types. Soil pH, the quantity and quality of organic C and NO3? content primarily determined N2O emissions. These results will likely assist modelling and mitigation of N2O emissions from different land use types in subtropical acidic soils in China and elsewhere.
Black carbon (BC) is considered to be a promising novel material for controlling organic contaminants due to its strong adsorption property, low production cost, and less secondary pollution. However, seldom systemic research was conducted to investigate adsorption-desorption characteristics and interaction mechanism between BC and nonylphenol (NP), one kind of endocrine-disrupting contaminants (EDCs) and persistent organic pollutants (POPs). Therefore, in the present study, adsorption characteristics of NP on two BCs (rice straw black carbon (RC) and fly ash carbon (FC)) involving adsorption isotherm, kinetics, effect of pH, as well as desorption kinetics, were investigated to explore the feasibility of BC for remediation of NP pollution in a water environment. Adsorption isotherm data showed that Qmax was 61,889.21 ± 2777.68 and 6538.99 ± 606.72 mg/kg and n was 0.39 ± 0.037 and 0.55 ± 0.043 for RC and FC, respectively, suggesting the sorption capacity and nonlinearity of RC to NP is far higher than FC and indicating BC was an effective sorbent for NP pollution control, especially RC. The pH affected BC sorption capacity to NP by influencing the surface properties of BC and the NP speciation together. Desorption kinetics data indicated that more than 80% NP could not be released from both BCs, suggesting that BC could reduce NP releasing risk in a water environment evidently when BC is applied for NP pollution remediation.
Amine-grafted MSU-3 mesoporous silica samples were synthesized from pure and waste silica sources and their CO2 adsorption performances were evaluated. The obtained samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), N2 adsorption–desorption isotherm analysis, Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). CO2 adsorption capacities of the samples at different temperatures were determined by TGA. The amine-modified MSU-3 synthesized from waste exhibited the highest CO2 adsorption capacity of 1.32 mmol/g at 25 °C and 1 bar, depending essentially on the porous texture and the amine content of the material. The CO2 adsorption isotherms of the synthesized samples were measured by a static volumetric method. Adsorption isotherm indicated that the amine-modified samples presented significantly higher CO2 adsorption capacity than the pure samples. The Avrami kinetic model fitted the experimental data well and suggested that complex reaction mechanism or the appearance of multiple reaction pathway occurred in the CO2 adsorption.
A better understanding of the role of grassland systems in producing and storing phytolith-occluded carbon (PhytOC) will provide crucial information in addressing global climate change caused by a rapid increase in the atmospheric CO2 concentration.
Materials and methods
Soil samples of typical steppe, meadow steppe, and meadow in Inner Mongolia, China, were taken at 0–10-, 10–20-, 20–40-, and 40–60-cm depths in July and August of 2015. The soil phytoliths were isolated by heavy liquid (ZnBr2), and the soil PhytOC was determined by the traditional potassium dichromate method.
Results and discussion
The results of our study showed that the storage of soil phytoliths was significantly higher in the meadow (33.44 ± 0.91 t ha?1) cf. meadow steppe (26.8 ± 0.98 t ha?1) and typical steppe (21.19 ± 4.91 t ha?1), which were not different. The soil PhytOC storage was significantly different among grassland types, being: meadow (0.39 ± 0.01 t ha?1) > meadow steppe (0.29 ± 0.02 t ha?1) > typical steppe (0.23 ± 0.02 t ha?1). PhytOC storage in typical steppe soil within the 0–60-cm soil layer is the lowest and that in meadow soils is the highest. The grassland type and the soil condition play significant roles in accumulation of phytoliths and PhytOC in different grassland soils. We suggest that the aboveground net primary productivity (ANPP) is important in soil phytolith accumulation and PhytOC content.
Conclusions
Phytolith and PhytOC storages in grassland soil are influenced by factors such as grass type, local climate and soil conditions, and management practices. Management practices to increase grass biomass production can significantly enhance phytolith C sequestration.
In this work, disks containing different amount of the TiO2 precursor impregnated on the raw red clay were produced. The disks were obtained by pressing in metal template and subsequently calcined at 500 °C. The raw clay was used as rigid support to fix the TiO2. The materials were characterized by X-ray diffraction, diffuse reflectance spectroscopy, N2 adsorption-desorption (BET and BJH), scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy. The ability of disks to produce superoxide and hydroxyl radicals after photoexcitation with UV irradiation was monitored by EPR. The catalytic efficiency was evaluated by the Reactive Red 141 dye discoloration under artificial UV light and sunlight. The reaction parameters such as concentration of RR-141 and irradiation source were evaluated. The results showed that the disks were able to decolorize 97.5% under sunlight at 60 min. The disks were also efficient in the discoloration until the tenth cycle, resulting in discoloration values near the initial cycles. Additionally, the dye fragments produced in cleavage of molecule during the reaction were evaluated by LC/MS-MS.
A bioadsorbent formulated with a secondary raw material, consisting of grape marc, subjected to a bioxidize process and entrapped in calcium alginate beads, was used for the desalination of water containing copper(II) sulfate. Experiments were established under different experimental conditions varying the concentration of contaminant, the amount of bioadsorbent, and the extraction time through response surface methodology. The most significant variable in the removal of copper(II) sulfate was the amount of bioadsorbent employed, followed by the extraction time; whereas, the adsorbent capacity was more influenced by the amount of contaminant and the amount of bioadsorbent used. At the highest concentration of copper(II) sulfate (0.15 mol/L), the equations obtained predict that the bioadsorbent has a capacity of 2785 mg/g and produces a copper(II) removal about 43% using low adsorbent/water ratios, 1:10 (v/v), and maximum extraction times; whereas, it would remove 97.2% of copper(II) sulfate in 5 min, using adsorbent/water ratios close to 1:2 (v/v), with capacity values, in this case, around 1800 mg/g. The encapsulation of the bioxidize adsorbent increased its capacity to 30% and allowed the precipitation of sulfate ions as calcium sulfate. The results obtained in this work could presume advances for promoting the industrial symbiosis between winery and environmental industries.
Graphical abstract Utilization of secondary raw material, consisting of bioxidize grape marc from winery industry, as bioadsorbent encapsulated in calcium alginate beads, for the removal of copper(II) sulfate from water
Calix[4]arene-crown-6 compounds are promising ligands in the removal of cesium. With this aim, a macrocyclic compound, calix[4]arene-crown-6, was chemically immobilized onto inorganic ordered mesoporous carbon material. Several adsorption parameters such as nitric acid concentration, contact time, initial cesium content, operation temperature, and competing ions were studied. The results demonstrated the prepared material conserved high cesium selectivity of calix[4]arene-crown-6 and physicochemistry stability of the ordered mesoporous carbon matrix and showed the superior cesium adsorption performance. The optimum adsorption acidity determined as 3.0 M nitric acid was consistent with the actual acidity value in the back-end of the nuclear fuel cycle. The Langmuir model indicated the monolayer coverage adsorption and the highest mass adsorption capacity was calculated as 128.06 mg cesium/g. The pseudo-second-order model and D-R model proved the adsorption was a chemical process. Thermodynamics parameters showed the adsorption was spontaneous and exothermal in nature. Competing ions hardly affected cesium adsorption. Furthermore, the adsorbent showed almost intact adsorption capacity after five adsorption-elution cycles. The comprehensive performance highlights the composite material as a promising adsorbent for cesium adsorption from wastewaters.
Better understanding of N transformations and the regulation of N2O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.
Materials and methods
15N tracer technique combined with acetylene (C2H2) method was used to measure gross N transformation rates and to distinguish pathways of N2O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.
Results and discussion
Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (ntot) was 7.28 mg N kg?1 day?1 in TR soil () and 5.79 mg N kg?1 day?1 in GN soil. Heterotrophic nitrification rates (nh), which accounting for 50.8 and 41.9% of ntot, and 23.4 and 30.1% of N2O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N2O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg?1 day?1 under selected conditions but contributed more than 30% of N2O emissions.
Conclusions
Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO3?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N2O emission in two pasture soils should be considered when developing mitigation strategies.
Effects of graphene oxide (GO) on phosphorus removal characteristics and mechanisms of aerobic granular sludge (AGS) were investigated in controlled batch tests. The scanning electron microscope (SEM) image results showed that the surface of AGS appeared wrinkled with coccus and bacillus brevis being wizened and the fungal mycelium being cut into pieces in AGS with 0.06 g/L GO. The anaerobic and aerobic batch tests suggested that the net phosphorus uptake of AGS was 2.60 mg/L for AGS with GO, compared with the value (4.38 mg/L) without GO, and the maximum release and uptake phosphorus rates also remarkably decreased. Intracellular and extracellular phosphorus contents were reduced to 64.67 and 19.74% of that without GO, indicating the nanoparticle might have great effects on extracellular phosphorus. The standards, measurements, and testing (SMT) analysis suggested that the inorganic phosphorus (IP) and organic phosphorus (OP) content decreased compared with the values without GO. The summation of phosphorus fraction associated with Ca (Ca-P) and the phosphorus fraction associated with Al, Fe, and Mn (Fe/Al-P) were 82.09% (without GO) and 94.27% (with GO), suggesting the presence of GO resulted in the decrease of content and species of IP. The extracellular polymeric substances (EPS) were reduced from 173.68 mg/g MLVSS to 137.55 mg/g MLVSS when AGS contacted with GO. The results of this assay had uncovered that 0.06 g/L GO could inhibit the bioactivity of phosphorus-accumulating organisms (PAOs), which resulted in the decrease of Ca-P, Fe/Al-P, and OP. EPS played an essential role on the phosphorus removal and granular stability. The decrease of EPS, which was produced by microorganisms, was contributed to decrease of extracellular phosphorus. This study provided an extensive insight into the influence of GO on phosphorus removal mechanism by AGS.
Occlusion of carbon in phytoliths is an important biogeochemical carbon sequestration mechanism and plays a significant role in the global biogeochemical carbon cycle and atmospheric carbon dioxide (CO2) concentration regulation at a millennial scale. However, few studies have focused on the storage of phytolith and phytolith-occluded carbon (PhytOC) in subtropical forest soils.
Materials and methods
Soil profiles with 100-cm depth were sampled from subtropical bamboo forest, fir forest, and chestnut forest in China to investigate the variation of phytoliths and PhytOC storage in the soil profiles based on amass-balance assessment.
Results and discussion
The storage of phytoliths in the top 100 cm of the bamboo forest soil (198.13?±?25.08 t ha?1) was much higher than that in the fir forest (146.76?±?4.53 t ha?1) and chestnut forest (170.87?±?9.59 t ha?1). Similarly, the storage of PhytOC in the bamboo forest soil (3.91?±?0.64 t ha?1) was much higher than that in the fir forest soil (1.18?±?0.22 t ha?1) and chestnut forest soil (2.67?±?0.23 t ha?1). The PhytOC percentage in the soil organic carbon pool increased with soil depth and was the highest (4.29 %) in the bamboo forest soil. Our study demonstrated that PhytOC in soil was significantly influenced by forest type and the bamboo forest ecosystem contributed more significantly to phytolith carbon sequestration than other forest ecosystems.
Conclusions
Different forest types have a significant influence on the soil PhytOC storage. Optimization of bamboo afforestation/reforestation in future forest management plans may significantly enhance the biogeochemical carbon sink in the following centuries.
Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH.
Materials and methods
Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg?1 (w/w), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH4+) and nitrate plus nitrite (NO3??+?NO2?).
Results and discussion
All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg?1 in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol(+) kg?1 compared to 2.82 and 4.19 cmol(+) kg?1 by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol(+) kg?1 per pH unit increase for both straws compared to 6.25 cmol(+) kg?1 per pH unit from the manure. The NO3??+?NO2? concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase.
Conclusions
While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.
Quarrying activities in areas with serpentinized rocks may have a negative impact on plant growth. Quarry soils generally offer hostile environments for plant growth due to their low-nutrient availability, low organic matter, and high-trace metal content.
Materials and methods
In order to determine the factors that can limit plant revegetation, this study was carried out in two serpentine quarries in Galicia (NW Spain): one abandoned in 1999 and the other still active.
Results and discussion
The results show that in soils developed in the abandoned quarry, the limitations for revegetation were: moderate alkaline pH (7.87–8.05), strong Ca/Mg (<1) imbalance, low N (<0.42 mg kg?1) and P (<2 mg kg?1) content, and high total heavy-metal content (Co 76–147 mg kg?1; Cr 1370–2600 mg kg?1; and Ni 1340–2040 mg kg?1). The limitations were much less intense in the soils developed in the substratum in the active quarry, which were incipient soils poorly developed and permanently affected by the quarrying activity.
Conclusions
Restoration work should be geared toward establishing a stable diverse vegetation cover, including serpentinophile species, which would provide the necessary modifications to correct nutritive imbalances and improve soil quality.
Heavy metals are a common contaminant in water supplies and pose a variety of serious health risks to nearby human populations. A promising approach to heavy metal decontamination is the sequestration of heavy metal ions in porous materials; however, current technologies involve materials which can be difficult to synthesize, are high-cost, or are themselves potentially toxic. Herein, we demonstrate that rapidly synthesized calcium carbonate (CaCO3) microparticles can effectively remove high quantities of Pb2+, Cd2+, and Cu2+ ions (1869, 1320, and 1293 mg per gram of CaCO3 microparticles, respectively) from aqueous media. The CaCO3 microparticles were characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer–Emmett–Teller (BET) N2 sorption–desorption. It was found that the Ca2+ ions of the microparticles were replaced by the heavy metal ions, leading to partially recrystallized nanoparticles of new compositional phases such as cerussite (PbCO3). The adsorption, surface dissolution/re-precipitation, and nucleation/crystal growth mechanisms were determined by investigating the Ca2+ released, along with the changes to particle morphology and crystal structure. Importantly, this study demonstrates that the porous CaCO3 microparticles performed well in a system with multiple heavy metal ion species: 100% of Cu2+, 97.5% of Pb2+, and 37.0% Cd2+ were removed from an aqueous solution of all cations with initial individual metal concentrations of 50 mg/L and 1.5 g/L of CaCO3 microparticles. At this concentration, the CaCO3 microparticles significantly outperformed activated carbon. These results help to establish CaCO3 microparticles as a promising low-cost and scalable technology for removing heavy metal ions from contaminated water.
