Removal of cadmium, copper, nickel, cobalt and mercury from water by Apatite II™: column experiments

Mobility and environmental impact of cadmium (Cd) during weathering of carbonaceous black shales in western Hunan, China

Carbonaceous black shale generally contains high concentration of Cd, with weathering leading to Cd release to environment. In this study, the mobility of Cd during weathering was quantified using geochemical assessment on black shale from western Hunan, China. Results suggested that Cd was heterogeneously distributed in shale profiles with concentrations ranging from 0.16 to 109.9 (mg/kg). Cd distribution was heterogeneous resulting from the parent shale inheritance and the mobility of Cd during weathering. Black shales weathered to a moderate degree with Cd mobility characterized by both enrichment in and release from weathered shales. Cd enrichment in weathered shales resulted from the re-enrichment of Cd in secondary minerals formed during the initial stage of carbonate (and phosphorite) dissolution, and the secondary stage of sulfide oxidation. The release of Cd was caused by decomposition of the secondary Cd-bearing minerals. Cadmium was extensively released during pedogenesis, and Cd release mass flux was estimated to range from 1.26 to 9.50 (g/m2) with a mean of 6.60 g/m2. Thus, black shale weathering may lead to the releasing of large amount of Cd resulting in Cd contamination to local environments.

Subaerial volcanism broke mid-Proterozoic environmental stasis

The mid-Proterozoic, spanning 1.8 to 0.8 billion years ago, is recognized as a phase of marine anoxia, low marine primary productivity (MPP), and constrained eukaryotic biodiversity. However, emerging evidence suggesting intermittent environmental disturbances and concurrent eukaryotic evolution challenges the notion of a stagnant Earth during this era. We present a study detailing volcanic activity and its consequential impact on terrestrial weathering and MPP, elucidated through the examination of 1.4-billion-year-old tropical offshore sediments. Our investigation, leveraging precise mercury (Hg) and lithium (Li) isotopic analyses, reveals the introduction of fresh rock substrates by local volcanism. This geological event initiated a transformative process, shifting the initial regolith-dominated condition in tropical lowland to a regime of enhanced chemical weathering and denudation efficiency. Notably, the heightened influx of nutrient-rich volcanic derivatives, especially phosphorus, spurred MPP rates and heightened organic carbon burial. These factors emerge as potential drivers in breaking the long-term static state of the mid-Proterozoic.

Co-precipitation of Cd with struvite during phosphorus recovery

During the struvite recovery process, Cd, a hazardous metal commonly found in waste streams, can be sequestered by struvite. This study investigated the influence of Cd2+ on the precipitation of struvite. Quantitative X-ray diffraction (QXRD) results showed that the purity of struvite decreased from 99.1% to 73.6% as Cd concentration increased from 1 to 500 μM. Scanning electron microscopy (SEM) revealed a roughened surface of struvite, and X-ray photoelectron spectroscopy (XPS) analysis indicated that the peak area ratio of Cd-OH increased from 19.4% to 51.3%, while the area ratio of Cd-PO4 decreased from 86.6% to 48.7% as Cd concentrations increased from 10 to 500 μM. The findings suggested that Cd2+ disrupted the crystal growth of struvite, and mainly combined with -OH and -PO4 to form amorphous Cd-bearing compounds co-precipitated with struvite. Additionally, Mg-containing amorphous phases were formed by incorporating Mg2+ with -OH and -PO4 during struvite formation.

Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives

With rapid industrial development and population growth, the pollution of soil and groundwater has become a critical concern all over the world. Yet, remediation of contaminated soil and water remains a major challenge. In recent years, apatite has gained a surging interest in environmental remediation because of its high treatment efficiency, low cost, and environmental benignity. This review summarizes recent advances in: (1) natural apatite of phosphate ores and biological source; (2) synthesis of engineered apatite particles (including stabilized or surface-modified apatite nanoparticles); (3) treatment effectiveness of apatite towards various environmental pollutants in soil and groundwater, including heavy metals (e.g., Pb, Zn, Cu, Cd, and Ni), inorganic anions (e.g., As oxyanions and F-), radionuclides (e.g., thorium (Th), strontium (Sr), and uranium (U)), and organic pollutants (e.g., antibiotics, dyes, and pesticides); and (4) the removal and/or interaction mechanisms of apatite towards the different contaminants. Lastly, the knowledge or technology gaps are identified and future research needs are proposed.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Surface functionalization with copper endows carbonate apatite honeycomb scaffold with antibacterial, proangiogenic, and pro-osteogenic activities

Osteomyelitis is a potentially devastating inflammatory bone disease that leads to bone destruction and loss. Treatment of osteomyelitis requires the removal of residual bacteria as well as osteogenesis with angiogenesis at the site of treatment. Use of an appropriate amount of copper (Cu) in treatment scaffolds may achieve these goals without the risk of toxicity. In this study, the surface of the carbonate apatite honeycomb scaffold was functionalized with Cu through a dissolution-precipitation reaction. The resulting scaffolds retained the honeycomb structure after immersion in CuCl₂ solution, and Cu was precipitated on the surface as libethenite [Cu₂(OH)PO₄]. The surface Cu concentration was controlled by the concentration of the CuCl₂ solution. Scaffolds with a surface Cu concentration of 23.8 wt% exhibited antibacterial and cytotoxic effects, whereas those with concentrations of ≤4.6 wt% exerted antibacterial effects without negatively affecting the cellular adhesion, proliferation, differentiation, and calcification of osteoblast-like cells. Furthermore, scaffolds with a surface Cu concentration of 4.6 wt% Cu inhibited bacterial growth for at least 28 days and displayed proangiogenic and pro-osteogenic activities in vivo. These data confirm the success in functionalizing scaffolds with Cu that may be utilized as an innovative osteomyelitis therapy.

Investigation of mercury(II) and copper(II) sorption in single and binary systems by alginate/polyethylenimine membranes

This study investigates Hg(II) and Cu(II) sorption in single and binary systems by alginate/polyethylenimine membranes. Batch experiments are conducted to assess the metal sorption performance. FTIR and SEM-EDX analyses are used to identify metal binding mechanism. The sorption kinetics are better fitted by the pseudo-second-order-equation compared to the pseudo-first-order-equation. Three isotherms are compared for fitting the sorption in mono-component solutions and the Sips model gives the best simulation of experimental data. The competitive-Sips model fits well sorption data in Hg-Cu binary solutions and finds that the Cu uptake is drastically reduced by Hg competition. Copper(II) uptake remains negligible at low pH whereas it increases with pH up to 6 because of material deprotonation. Mercury(II) sorption behaves differently, it slightly changes from pH 1 (q_eq: 0.76 mmol g^-1) to pH 6 (q_eq: 0.84 mmol g^-1) due to chloro-anion formation. Therefore, playing with the pH allows separating Hg(II) from Cu(II).

Enhanced removal of zinc and cadmium from water using carboxymethyl cellulose-bridged chlorapatite nanoparticles

Zinc (Zn²⁺) and cadmium (Cd²⁺) in water pose serious threats to human health and the environment. In search for a more effective treatment technology, we prepared a type of carboxymethyl cellulose (CMC) bridged chlorapatite (CMC-CAP) nanoparticles and tested the material for removal of Zn²⁺ and Cd²⁺ from water. CMC macromolecules were attached to CAP by bidentate bridging and hydrogen bonding, preserving the high adsorption capacity of CAP nanoparticles while allowing for easy gravity-separation of the nanoparticles. CMC-CAP showed rapid adsorption kinetics and 22.8% and 11.2% higher equilibrium uptake for Zn²⁺ and Cd²⁺, respectively, than pristine CAP. An extended dual-mode isotherm model, which takes into account both sorption and chemical precipitation, provided the best fits to the sorption isotherms, giving a maximum Langmuir sorption capacity of 141.1 mg g^-1 for Zn²⁺ and 150.2 mg g^-1 for Cd²⁺ by CMC-CAP. Na⁺ at up to 5 mM showed modest effects on the uptake of the heavy metals, while 2-5 mM of Ca²⁺ exerted notable inhibitive effects. Dissolved organic matter (up to 5 mg L^-1 as TOC) inhibited the Zn²⁺ uptake by 16.5% but enhanced the Cd²⁺ removal by 8.6%. Material characterizations and surface binding analyses revealed that ion exchange, surface precipitation, and surface complexation were the removal mechanisms for the heavy metals. This study demonstrates stabilizer bridging may serve as a convenient strategy to facilitate water treatment uses of nanoparticles.

Application of Nanoparticles Alleviates Heavy Metals Stress and Promotes Plant Growth: An Overview

Nanotechnology is playing a significant role in addressing a vast range of environmental challenges by providing innovative and effective solutions. Heavy metal (HM) contamination has gained considerable attention in recent years due their rapidly increasing concentrations in agricultural soil. Due to their unique physiochemical properties, nanoparticles (NPs) can be effectively applied for stress alleviation. In this review, we explore the current status of the literature regarding nano-enabled agriculture retrieved from the Web of Science databases and published from January 2010 to November 2020, with most of our sources spanning the past five years. We briefly discuss uptake and transport mechanisms, application methods (soil, hydroponic and foliar), exposure concentrations, and their impact on plant growth and development. The current literature contained sufficient information about NPs behavior in plants in the presence of pollutants, highlighting the alleviation mechanism to overcome the HM stress. Furthermore, we present a broad overview of recent advances regarding HM stress and the possible mechanism of interaction between NPs and HM in the agricultural system. Additionally, this review article will be supportive for the understanding of phytoremediation and micro-remediation of contaminated soils and also highlights the future research needs for the combined application of NPs in the soil for sustainable agriculture.

Adsorption of cadmium using modified zeolite-supported nanoscale zero-valent iron composites as a reactive material for PRBs

The main challenge in utilizing permeable reactive barriers (PRB) for remediation of metals-contaminated groundwater is determination of a proper low-cost reactive medium that can remove the desired contaminants simultaneously. In this study, the performance of different zeolite materials and nZVI-based adsorbents for cadmium (Cd) removal was compared. Further, a composite of the best nZVI and zeolite samples was synthesized with the removal efficiency of 20.6 g/kg and selected as the proposed adsorbent. Moreover, the characteristics of the composite were analyzed through different techniques (BET, XRF, XRD, FT-IR, FE-SEM and EDX). In addition, through kinetic and thermodynamic studies, the effect of temperature, pH, ionic strength and presence of other metal ions on Cd removal efficiency was investigated. According to the results, since sodium zeolite (NaZ) provides a large number of specific ion-exchange sites for decoration with nZVI, stabilizes nZVI, and prevents its aggregation and further leaching in the harsh environment, the NaZ-nZVI composite is capable of removing Cd by adsorption and is applicable in PRBs, and thus it seems that the aforementioned composite is a proper candidate for groundwater remediation from a wide range of metal ions.

Poultry litter ash characterisation and recovery

This paper reports a complete characterisation of poultry litter ash and its potential use as a heavy metal stabiliser. We propose a novel approach, in which the ashes deriving from municipal solid waste incineration (MSWI) are combined with poultry litter ash, rather than with coal combustion flue gas desulfurisation (FGD) residues. Heavy metals stabilisation was demonstrated by comparing the elemental concentrations in the leaching solutions of the starting raw and stabilised materials: leachable Pb and Zn showed a reduced solubility. The characterisation was conducted by total reflection X-ray fluorescence (TXRF), X-ray diffraction (XRD), micro-Raman spectroscopy and scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDX). The results showed that the poultry litter ash was Ca-, P-, K- and S-rich (>29 g/kg). It contained amorphous materials (i.e. fly ash economiser (FAECO) 73% and fly ash cyclone (FACYC) 61%) and soluble phases (e.g. arkanite and sylvite; up to 13% FAECO and 28% FACYC), as well as resilient crystalline (up to 2% of FAECO and FACYC) and amorphous phases (e.g. hydroxyapatite). After two months, the Pb and Zn concentrations in the leachate solutions were below the limit set by the European regulations for waste disposal (<0.2 mg/L and 1.5 mg/L, respectively). We propose a mechanism for the heavy metals stabilisation based on the carbonation process and high amounts of P, Ca and reactive amorphous phases. In conclusion, it is demonstrated that poultry litter ash can be an effective secondary source of heavy metals, allowing their immobilisation through P- and Ca-based reactive amorphous phases.

Natural fluorapatite dissolution kinetics and Mn2+ and Cr3+ metal removal from sulfate fluids at 35 °C

In light of the consequences of global warming and population growth, access to safe drinking water becomes an ever greater challenge, in particular in low to middle income countries in arid regions. Moreover, mining which may cause acid mine drainage and heavy metal contamination puts further pressure on management of limited water resources. Hence, the development of cost effective water treatment methods is critical. Here, using batch reactor experiments we investigate the kinetics and mechanisms behind divalent Mn and trivalent Cr removal from sulfate fluids using natural fluorapatite at 35 °C. The results show that the fluorapatite dissolution rate depends on fluid pH, and that dissolution is the dominant mechanism in fluids with pH below 4. Apatite can thus serve as remediation to neutralize acidic fluids. Fluid pH of 4-6 triggers a dissolution-precipitation mechanism, in some cases following upon a dissolution-only period, with the formation of a metal phosphate. In these experiments, Cr removal is two to ten times faster than Mn removal given similar solution pH. The results demonstrate that natural apatite represents a promising, cost effective material for use in passive remediation of mining-induced contamination of soils and groundwater in arid regions.

Waiting for Aπαταω: 250 Years Later

Scientific articles have been traditionally written from single points of view. In contrast, new knowledge is derived strictly from a dialectical process, through interbreeding of partially disparate perspectives. Dialogues, therefore, present a more veritable form for representing the process behind knowledge creation. They are also less prone to dogmatically disseminate ideas than monologues, alongside raising awareness of the necessity for discussion and challenging of differing points of view, through which knowledge evolves. Here we celebrate 250 years since the discovery of the chemical identity of the inorganic component of bone in 1769 by Johan Gottlieb Gahn through one such imaginary dialogue between two seasoned researchers and aficionados of this material. We provide the statistics on ups and downs in the popularity of this material throughout the history and also discuss important achievements and challenges associated with it. The shadow of Samuel Beckett's Waiting for Godot is cast over the dialogue, acting as its frequent reference point and the guide. With this dialogue presented in the format of a play, we provide hope that conversational or dramaturgical compositions of scientific articles - albeit virtually prohibited from the scientific literature of the day - may become more pervasive in the future.

Silver/quartz nanocomposite as an adsorbent for removal of mercury (II) ions from aqueous solutions

Silver nanoparticles (AgNPs) and silver/quartz nanocomposite (Ag/Q)NPs)) were synthesized by sol-gel method using table sugar as chelating agent. The synthesized nanosized materials were used for mercury ions adsorption from aqueous solutions. The materials were characterized by X-ray diffraction (XRD), Transmission Electron microscope (TEM), and surface area (BET). Adsorption of Hg²⁺ (10 mg/l) is strongly dependent on time, initial metal concentration, dose of adsorbent and pH value. Silver/quartz nanocomposite ((Ag/Q)NPs)) shows better efficiency than individual silver nanoparticles (AgNPs). This composite removed mercury ions from the aqueous solution with efficiency of 96% at 60 min with 0.5g adsorbent dosage at pH 6. The adsorption process explained well by the pseudo-second-order kinetic model. In conclusion silver/quartz nanocomposite (Ag/Q)NPs)) shows higher removal efficiency for mercury ions from aqueous solutions than individual silver naoparticles (AgNPs) or quartz (Q).

Phosphate amendments for chemical immobilization of uranium in contaminated soil

Uranium (U) contamination is a major environmental problem associated with the mining and processing of nuclear materials for both weapons and power production. When possible, in situ soil remediation techniques are preferable for reducing the risk associated with diffuse low-level U contamination. Uranium is known to form sparingly soluble phosphate compounds that persist in the environment. Therefore, batch experiments were performed to evaluate the efficacy of three phosphate amendments, hydroxyapatite (HA), sodium phytate (IP6) and sodium tripolyphosphate (TPP), to immobilize U in contaminated sediments. The amendments were added at equivalent phosphorus (P) concentrations and then equilibrated under a range of test conditions, with changes in soluble U and P_total monitored at pre-set time intervals. Only HA was effective at reducing the soluble U soil fraction when compared to the control, with IP6 and TPP increasing the soluble U soil fraction. After equilibration, changes in contaminant partitioning in the amended sediments were evaluated using operational extraction methods. Sequential extraction results for HA generally indicated a transfer of U from labile to more recalcitrant phases, while the results for IP6 and TPP were more ambiguous.

Immobilization of radioactive corrosion products by cold sintering of pure hydroxyapatite

An efficient method for the consolidation of cobalt (Co(II)) adsorbed calcium hydroxyapatite was investigated to develop a simplified route for decontamination of the coolant system of nuclear power plants and direct immobilization of as-spent adsorbent. Calcium hydroxyapatite nano-powder synthesized by a wet precipitation method was used as an adsorbent and 94% Co(II) surrogate removal from simulated water was measured. The as-spent adsorbent was sintered at 200 °C, a temperature significantly lower than conventional sintering temperatures (900-1300 °C) for hydroxyapatite, under a uniaxial pressure of 500 MPa for 10 min. The relative density after the cold sintering was >97% and sintered samples displayed good compressive strength (175 MPa). The normalized leaching rate of the Co(II) was measured as per ASTM-C1285 standard and found to be 2.5 × 10^-5 g/m²/day. ANSI/ANS-16.1 test procedure was used to analyze the leachability of the sintered matrices and the measured leaching index value was 6.5. Thus, the use of pure calcium hydroxyapatite nano-powder as adsorbent and its cold sintering offers a mean by which radioactive waste form can be processed in an environment friendly manner.

Effect of vegetables and nano-particle hydroxyapatite on the remediation of cadmium and phosphatase activity in rhizosphere soil through immobilization

Nano-hydroxyapatite (n-HAP) and two types of plants (rape plant and cabbage) were used in this study to investigate their combined remediation effect on the removal of heavy metal contaminated soil. Different n-HAP concentrations (5, 10, 15, 20, and 25 g kg^-1) with two kinds of plants were used in the experiments and compared with two control groups without adding n-HAP. Compared with the control group, the total Cd concentration increased and the amount of available Cd decreased significantly in soil (p < 0.05) in text groups. Cd toxicity decreased, and the rape plant and cabbage biomass increased after adding n-HAP. Cd accumulation in rape plant and cabbage decreased when more n-HAP was added; Cd accumulated less in rape plant than in cabbage. The phosphatase activity in soil also increased after adding n-HAP. Results showed that the total Cd concentration was positively correlated with phosphatase activity, the concentration of the available Cd and Cd accumulated in root has a significant effect on phosphatase activity in Cd-contaminated soil (p < 0.05). Cd-contaminated soil could be remediated effectively with rape plant and n-HAP with a concentration of 15 g kg^-1.

The use of calcium carbonate-enriched clay minerals and diammonium phosphate as novel immobilization agents for mercury remediation: Spectral investigations and field applications

We used calcium carbonate-enriched clay minerals (CECM) and diammonium phosphate (DAP) as immobilization agents for mercury (Hg) immobilization. The effects of CECM, DAP, or both in different amounts and ratios, as well as pH and initial Hg concentrations, on Hg removal from solutions were investigated. The removal mechanism was revealed using transmission electron microscope with energy-dispersive X-ray (TEM-EDX) spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The performance of CECM and DAP under field conditions was also studied. The results showed that application of CECM and DAP at a ratio of 50:1 (w/w) removed over 90% of Hg from solutions containing 1.8 μM Hg²⁺, which was 9- or 2.6-fold higher than solely DAP (<10%) or CECM (34%<), respectively. Mercury removal by CECM and DAP was weakly affected by pH values between 4 and 10, and their maximum Hg removal capacity was 37 mg g^-1. Both TEM-EDX and EXAFS results showed that the precipitate of Hg with phosphorus-associated minerals might be the primary mechanism of Hg removal by CECM and DAP. Results from the field trial showed that application of CECM and DAP decreased soil bioavailable Hg contents, but did not affect contents of organic matter bound Hg or residual Hg fractions, as compared with control and initial soils. Application of CECM and DAP resulted in dramatic reductions (40%-53%) of Hg in the edible tissues of Brassica chinensis and Raphanus raphanistrum in comparison to the non-treated control. We conclude that CECM and DAP offer a promising method for in situ remediation of Hg-contaminated farmlands in southwest of China.

Immobilization of cesium from aqueous solution using nanoparticles of synthetic calcium phosphates

The particularities of cesium incorporation into synthetic calcium phosphates with either apatite or whitlockite-type structures were investigated using the sorption process from aqueous solution and further heating to 700 °C. The nanoparticles for sorption were prepared by wet precipitation from aqueous solutions at a fixed molar ratio of Ca/P = 1.67 and two different ratios of CO₃²⁻/PO₄³⁻ (0 or 1). The obtained substituted calcium phosphates and corresponding samples after the sorption of cesium from solutions with different molar concentrations (c(Cs⁺) = 0.05, 0.1 and 0.25 mol L⁻¹) were characterized by powder X-ray diffraction, FTIR spectroscopy, scanning electron microscopy and elemental analysis. Based on the combination of X-ray diffraction and elemental analyses data for the powders after sorption, the cesium incorporated in the apatite- or whitlockite-type structures and its amount increased with its concentration in the initial solution. For sodium-containing calcium phosphate even minor content of Cs⁺ in its composition significantly changed the general principle of its transformation under annealing at 700 °C with the formation of a mixture of α-Ca₃(PO₄)₂ and cesium-containing apatite-related phase. The obtained results indicate the perspective of using of complex substituted calcium phosphates nanoparticles for immobilization of cesium in the stable whitlockite- or apatite-type crystal materials.

Effect of nanohydroxyapatite on cadmium leaching and environmental risks under simulated acid rain

Cadmium (Cd) contamination in soil is a global environmental pollution issue. Nanohydroxyapatite (NHAP) has been used in soil remediation to immobilize cadmium in contaminated soils. However, the effect of acid rain on the export of cadmium from topsoil and its behavior in deep soil and leachate is unclear. In this study, column experiments and development of parsimonious model were performed to estimate Cd leaching behavior from topsoil and environmental risk of groundwater after 0.5% NHAP remediation. Four leaching events were performed and total Cd, different fractions of Cd determined by sequential extraction procedure and pH were determined for each leaching. The results show that with the export of Cd in topsoil, the total Cd concentration in soil at different depths had the following vertical distributions: 0-5 cm > 5-10 cm > 10-15 cm > 15-20 cm. NHAP treatment increased the soil pH and decreased Cd leaching loss by 56.45% compared to the control, and the results fit the parabolic diffusion model. With sequential extraction it was observed that NHAP application increased the residual fraction of cadmium in soil. After leaching, there was a positive correlation between soil pH and Cd concentration with regards to the exchangeable, reducible, oxidizable and residual Cd fractions. The parabolic diffusion model showed that Cd-contaminated soil with NHAP remediation is harmless to humans after sufficient remediation duration, whereas the resultant concentrations from the CK treatment could be toxic. The results indicate that nanohydroxyapatite could significantly reduce the bioavailability of cadmium and the environmental risk. However, the release of Ca and P from the dissolution of NHAP should be carefully studied as this will impact the mobilization of Cd or colloid Cd, and high leaching of P may result in P-induced eutrophication risk.

Long-Term Quantitative Evaluation of Muscle and Bone Wasting Induced by Botulinum Toxin in Mice Using Microcomputed Tomography

Muscle and bone masses are highly correlated and muscles impose large loads on bone. Muscle wasting that accompanies bone loss has been poorly investigated. 21 female mice were spread into seven groups. At day 0, 18 mice received Botulinum toxin (BTX) injection in the quadriceps muscle to induce paralysis of the right hind limb; the left contralateral side was used as control. Mice were sacrificed at 7, 14, 21, 28, 56 and 90 days post-injection. A remaining group was sacrificed at day 0. Trabecular bone volume was determined by microcomputed tomography (microCT) at the distal femur and tibia proximal metaphyses on both sides. Limbs were immersed in an HgCl₂ solution allowing muscle visualization by microCT. On 2D sections, the cross-sectional areas and form-factors were measured for the quadriceps at mid-thigh and gastrocnemius at mid-leg and these muscles were dissected and weighed. Bone volume decreased in the paralysed side. Bone loss was maximal at 56 days followed by recuperation at 90 days. The cross-sectional areas of gastrocnemius and quadriceps were significantly lower in the paralysed limb from 7 days; the decrease was maximum at 21 days for the gastrocnemius and 28 days for the quadriceps. No difference in form-factors was found between the two limbs. Similar results were obtained with the anatomical method and significant correlations were obtained between the two methods. Quantitative analysis of muscle loss and recovery was possible by microCT after using a metallic contrast agent. Loss of bone secondary to muscle wastage induced by BTX and recovery showed a parallel evolution for bone and muscles.

Direct Observation of Simultaneous Immobilization of Cadmium and Arsenate at the Brushite-Fluid Interface

Cadmium (Cd²⁺) and Arsenate (As⁵⁺) are the main toxic elements in soil environments and are easily taken up by plants. Unraveling the kinetics of the adsorption and subsequent precipitation/immobilization on mineral surfaces is of considerable importance for predicting the fate of these dissolved species in soils. Here we used in situ atomic force microscopy (AFM) to image the dissolution on the (010) face of brushite (dicalcium phosphate dihydrate, CaHPO₄·2H₂O) in CdCl₂- or Na₂HAsO₄-bearing solutions over a broad pH and concentration range. During the initial dissolution processes, we observed that Cd or As adsorbed on step edges to modify the morphology of etch pits from the normal triangular shape to a four-sided trapezium. Following extended reaction times, the respective precipitates were formed on brushite through a coupled dissolution-precipitation mechanism. In the presence of both CdCl₂ and Na₂HAsO₄ in reaction solutions at pH 8.0, high-resolution transmission electron microscopy (HRTEM) showed a coexistence of both amorphous and crystalline phases, i.e., a mixed precipitate of amorphous and crystalline Cd_{(5- x)}Ca _x(AsO₄)_{(3- y)}(PO₄) _yOH phases was detected. These direct dynamic observations of the transformation of adsorbed species to surface precipitates may improve the mechanistic understanding of the calcium phosphate mineral interface-induced simultaneous immobilization of both Cd and As and subsequent sequestration in diverse soils.

Efficient removal of Hg2+ in aqueous solution with fishbone charcoal as adsorbent

The Hg²⁺ removal performance of fishbone charcoal prepared from discarded fishbone has been investigated in this work. The XRD, FTIR, and BET results demonstrated that the main composition of fishbone charcoal was hydroxyapatite and the specific surface area was 117 m²/g. The adsorption experiments indicated that fishbone charcoal had an extremely high adsorption capacity for Hg²⁺ (243.77 mg/g). The excellent Hg²⁺ adsorption capacity might be ascribed to the ion exchange of Hg²⁺ to the Ca²⁺ in the structure of fishbone charcoal, complexation of Hg²⁺ with ≡Ca(OH)²⁺ on the surface of fishbone charcoal, as well as electrostatic interaction between electronegative fishbone charcoal surface and cation Hg²⁺. This work transformed kitchen garbage (i.e., fishbone) into an effective mercury adsorbent with considerable capacity, giving a perspective sight for the utilization of solid waste.

Preparation and characterization of mesoporous hydroxyapatite with non-cytotoxicity and heavy metal adsorption capacity

Mesoporous hydroxyapatite (MPHA) particles have recently gained a great deal of interest in a broad range of fields including biomedical fields, wastewater treatment and catalysis.

Ionic Strength Differentially Affects the Bioavailability of Neutral and Negatively Charged Inorganic Hg Complexes

Mercury (Hg) bioavailability to bacteria in marine systems is the first step toward its bioamplification in food webs. These systems exhibit high salinity and ionic strength that will both alter Hg speciation and properties of the bacteria cell walls. The role of Hg speciation on Hg bioavailability in marine systems has not been teased apart from that of ionic strength on cell wall properties, however. We developed and optimized a whole-cell Hg bioreporter capable of functioning under aerobic and anaerobic conditions and exhibiting no physiological limitations of signal production to changes in ionic strength. We show that ionic strength controls the bioavailability of Hg species, regardless of their charge, possibly by altering properties of the bacterial cell wall. The unexpected anaerobic bioavailability of negatively charged halocomplexes may help explain Hg methylation in marine systems such as the oxygen-deficient zone in the oceanic water column, sea ice or polar snow.

Kinetic and thermodynamic studies of the Co(II) and Ni(II) ions removal from aqueous solutions by Ca-Mg phosphates

The aim of this work was to study the sorption kinetics and thermodynamics of Co(II) and Ni(II) from aqueous solutions by sorbents on the basis of hydrogen (PD-1) and tertiary (PD-2) Ca-Mg phosphates depending on the solution temperature and sorbents chemical composition. Kinetic studies of adsorption of Co(II) and Ni(II) ions onto samples of phosphate sorbents were performed in batch experiment at the temperatures 288, 303, 318 and 333 K. The sorbent dose was fixed at 10 g L^-1, initial pH value 2.6, and contact time varied from 5 to 600 min. The kinetics of Co(II) and Ni(II) adsorption were analyzed by using pseudo-first order, pseudo-second order and intraparticle diffusion models. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) for the sorption of Co(II) and Ni(II) were determined using the Gibbs-Helmholtz equation. The calculated kinetic parameters and corresponding correlation coefficients revealed that Co(II) and Ni(II) uptake process followed the pseudo-second order rate expression. Thermodynamic studies confirmed the spontaneous and endothermic nature of removal process which indicate that sorption of Co(II) and Ni(II) ions onto both phosphate sorbents is favoured at higher temperatures and has the chemisorptive mechanism. The data thus obtained would be useful for practical application of the low cost and highly effective Ca-Mg phosphate sorbents.

Sorption performances of TiO(OH)(H2PO4)·H2O in synthetic and mine waters

The first report on sorption behaviour of a titanium phosphate sorbent containing entirely –H₂PO₄ groups reveals a high exchange capacity and fast kinetics.

Calcium Phosphate as a Key Material for Socially Responsible Tissue Engineering

Socially responsible technologies are designed while taking into consideration the socioeconomic, geopolitical and environmental limitations of regions in which they will be implemented. In the medical context, this involves making therapeutic platforms more accessible and affordable to patients in poor regions of the world wherein a given disease is endemic. This often necessitates going against the reigning trend of making therapeutic nanoparticles ever more structurally complex and expensive. However, studies aimed at simplifying materials and formulations while maintaining the functionality and therapeutic response of their more complex counterparts seldom provoke a significant interest in the scientific community. In this review we demonstrate that such compositional simplifications are meaningful when it comes to the design of a solution for osteomyelitis, a disease that is in its natural, non-postoperative form particularly prevalent in the underdeveloped parts of the world wherein poverty, poor sanitary conditions, and chronically compromised defense lines of the immune system are the norm. We show that calcium phosphate nanoparticles, which are inexpensive to make, could be chemically designed to possess the same functionality as a hypothetic mixture additionally composed of: (a) a bone growth factor; (b) an antibiotic for prophylactic or anti-infective purposes; (c) a bisphosphonate as an antiresorptive compound; (d) a viral vector to enable the intracellular delivery of therapeutics; (e) a luminescent dye; (f) a radiographic component; (g) an imaging contrast agent; (h) a magnetic domain; and (i) polymers as viscous components enabling the injectability of the material and acting as carriers for the sustained release of a drug. In particular, calcium phosphates could: (a) produce tunable drug release profiles; (b) take the form of viscous and injectable, self-setting pastes; (c) be naturally osteo-inductive and inhibitory for osteoclastogenesis; (d) intracellularly deliver bioactive compounds; (e) accommodate an array of functional ions; (f) be processed into macroporous constructs for tissue engineering; and (g) be naturally antimicrobial. All in all, we see in calcium phosphates the presence of a protean nature whose therapeutic potentials have been barely tapped into.

The role of nano-sized manganese coatings on bone char in removing arsenic(V) from solution: Implications for permeable reactive barrier technologies

Although the removal of arsenic(V) (As(V)) from solution can be improved by forming metal-bearing coatings on solid media, there has been no research to date examining the relationship between the coating and As(V) sorption performance. Manganese-coated bone char samples with varying concentrations of Mn were created to investigate the adsorption and desorption of As(V) using batch and column experiments. Breakthrough curves were obtained by fitting the Convection-Diffusion Equation (CDE), and retardation factors were used to quantify the effects of the Mn coatings on the retention of As(V). Uncoated bone char has a higher retention factor (44.7) than bone char with 0.465 mg/g of Mn (22.0), but bone char samples with between 5.02 mg/g and 14.5 mg/g Mn have significantly higher retention factors (56.8-246). The relationship between retardation factor (Y) and Mn concentration (X) is Y = 15.1 X + 19.8. Between 0.2% and 0.6% of the sorbed As is desorbed from the Mn-coated bone char at an initial pH value of 4, compared to 30% from the uncoated bone char. The ability of the Mn-coated bone char to neutralize solutions increases with increased amounts of Mn on the char. The results suggest that using Mn-coated bone char in Permeable Reactive Barriers would be an effective method for remediating As(V)-bearing solutions such as acid mine drainage.

Cd-Resistant Strains of B. cereus S5 with Endurance Capacity and Their Capacities for Cadmium Removal from Cadmium-Polluted Water

The goal of this study was to identify Cd-resistant bacterial strains with endurance capacity and to evaluate their ability to remove cadmium ions from cadmium-polluted water. The Bacillus cereusS5 strain identified in this study had the closest genetic relationship with B. cereus sp. Cp1 and performed well in the removal of Cd²⁺ions from solution. The results showed that both the live and dead biomasses of the Cd²⁺-tolerant B. cereus S5 strain could absorb Cd²⁺ ions in solution but that the live biomass of the B. cereus S5 strain outperformed the dead biomass at lower Cd²⁺concentrations. An analysis of the cadmium tolerance genes of B. cereus S5 identified ATPase genes that were associated with cadmium tolerance and involved in the ATP pumping mechanism. The FTIR spectra revealed the presence of amino, carboxyl and hydroxyl groups on the pristine biomass and indicated that the cadmium ion removal ability was related to the structure of the strain. The maximum absorption capacity of the B. cereus S5 strain in viable spore biomass was 70.16 mg/g (dry weight) based on a pseudo-second-order kinetic model fit to the experimental data. The Langmuir and Langmuir-Freundlich isotherm adsorption models fit the cadmium ion adsorption data well, and the kinetic curves indicated that the adsorption rate was second-order. For Cd²⁺ concentrations (mg/L) of 1–109 mg/L, good removal efficiency (>80%) was achieved using approximately 3.48–10.3 g/L of active spore biomass of the B. cereus S5 strain. A cadmium-tolerant bacteria-activated carbon-immobilized column could be used for a longer duration and exhibited greater treatment efficacy than the control column in the treatment of cadmium-polluted water. In addition, a toxicity assessment using mice demonstrated that the biomass of the B. cereus S5 strain and its fermentation products were non-toxic. Thus, the isolated B. cereus S5 strain can be considered an alternative biological adsorbent for use in emergency responses to severe cadmium pollution and in the routine treatment of trace cadmium pollution.

Removal of mercury by adsorption: a review

Due to natural and production activities, mercury contamination has become one of the major environmental problems over the world. Mercury contamination is a serious threat to human health. Among the existing technologies available for mercury pollution control, the adsorption process can get excellent separation effects and has been further studied. This review is attempted to cover a wide range of adsorbents that were developed for the removal of mercury from the year 2011. Various adsorbents, including the latest adsorbents, are presented along with highlighting and discussing the key advancements on their preparation, modification technologies, and strategies. By comparing their adsorption capacities, it is evident from the literature survey that some adsorbents have shown excellent potential for the removal of mercury. However, there is still a need to develop novel, efficient adsorbents with low cost, high stability, and easy production and manufacture for practical utility.