Efficient bio-cementation between silicate tailings and biogenic calcium carbonate: Nano-scale structure and mechanism of the interface.

Biogenic calcium carbonate (bio-CaCO3) cementing tailings is an efficient technology to immobilize heavy metals in waste tailings. However, the underlying mechanism of interface cementation has not yet been clearly established, which limits the technological development. In this study, we used advanced techniques, including atomic force microscopy-based Lorentz contact resonance (AFM-LCR) spectroscopy, AFM-based nanoscale infrared (AFM-IR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy, to reveal the structural, mechanical, and chemical properties of the interface on the nanoscale. Ureolytic bacteria produced bio-CaCO3 to fill in pore space and to bind cement tailings particles, which prevented the formation of leachate containing heavy metals. After cementation, a strong 40-300 nm thin interface was formed between the taillings and bio-CaCO3 particles. Unlike chemically synthesized CaCO3, bio-CaCO3 is strongly negatively charged, which gives it better adhesion ability. Fourier transform infrared (FTIR), AFM-IR, and 29Si ssNMR spectra indicated that the Si-OH and Si-O-Si groups on the silicate surface were converted to deprotonated silanol groups (≡Si-O-) at a high pH and they formed strong chemical bonds of Si-O-Ca on the interface through a Ca ion bridge. In addition, hydrogen bonding with Si-OH also played a role at the cementation interface. These findings provide the nano-scale interfacial structure and mechanism of bio-CaCO3 cementing silicate tailings and accelerate the development of tailings disposal technology.

Innovative Homo sapiens behaviours 105,000 years ago in a wetter Kalahari.

The archaeological record of Africa provides the earliest evidence for the emergence of the complex symbolic and technological behaviours that characterize Homo sapiens1-7. The coastal setting of many archaeological sites of the Late Pleistocene epoch, and the abundant shellfish remains recovered from them, has led to a dominant narrative in which modern human origins in southern Africa are intrinsically tied to the coast and marine resources8-12, and behavioural innovations in the interior lag behind. However, stratified Late Pleistocene sites with good preservation and robust chronologies are rare in the interior of southern Africa, and the coastal hypothesis therefore remains untested. Here we show that early human innovations that are similar to those dated to around 105 thousand years ago (ka) in coastal southern Africa existed at around the same time among humans who lived over 600 km inland. We report evidence for the intentional collection of non-utilitarian objects (calcite crystals) and ostrich eggshell from excavations of a stratified rockshelter deposit in the southern Kalahari Basin, which we date by optically stimulated luminescence to around 105 ka. Uranium-thorium dating of relict tufa deposits indicates sporadic periods of substantial volumes of fresh, flowing water; the oldest of these episodes is dated to between 110 and 100 ka and is coeval with the archaeological deposit. Our results suggest that behavioural innovations among humans in the interior of southern Africa did not lag behind those of populations near the coast, and that these innovations may have developed within a wet savannah environment. Models that tie the emergence of behavioural innovations to the exploitation of coastal resources by our species may therefore require revision.

Synthesis and assessment of metallic ion migration through a novel calcium carbonate coating for biomedical implants.

Titanium (Ti) implants are commonly regarded as well accepted by the body. However, metal ion release is still a cause for concern. A small decrease in pH, which can be caused by inflammation, may produce a large increase in the corrosion rate of Ti implants. Coating the alloy with a buffer layer could have a significant protective effect. In this study, a calcium carbonate coating was developed on commercially pure Ti and a Ti-6Al-4V alloy through a hydrothermal treatment of previously NaOH-treated surfaces in calcium-citric acid chelate complexes. The results showed that a superstructured calcite coating layer formed on the Ti substrate after treatment at 170°C for 3 hr. The coating was approx. 1 µm thick and covered the substrate surface uniformly. When prolonging the hydrothermal treatment from 5 hr to 24 hr, the rhombohedral structure of calcite was observed in addition to the superstructure of calcite. Dissolution test results showed no significant differences in solution pH between the coated- and un-coated samples. However, the CaCO3 coating reduced by approx. 2-5 times the Ti and V ion release from the substrate as compared to the uncoated material, at pH 4. CaCO3 and hydroxyapatite (HA) coatings gave nonsignificant effects at neutral pH although the HA coating showed a trend for better results at the longer time points. The reduction in metal ion release from the substrate and the buffering ability of the CaCO3 coating encourage further studies on this coating for clinical applications.

Assessment of iron-modified calcite/zeolite mixture as a capping material to control sedimentary phosphorus and nitrogen liberation.

Calcite/zeolite mixture (CZ) can be used to construct a capping layer for the simultaneous management of phosphorus (P) and nitrogen (N) liberation from sediments into the overlying water (OVER-water). However, its control efficiency of sedimentary P release still needs to be improved. To address this issue, an iron-modified CZ (Fe-CZ) was synthesized, characterized, and employed as a capping material to simultaneously prevent P and N release from sediments into OVER-water. Batch and microcosm incubation experiments were performed to study the efficiency and mechanism for the control of P and N release from sediments by capping Fe-CZ. Results showed that sediment capping with Fe-CZ resulted in the significant reduction of soluble reactive P (SRP) and ammonium-N (NH3-N) in OVER-water, with reduction rates of 77.8-99.7% and 54.0-96.7%, respectively. Furthermore, the Fe-CZ capping layer decreased the SRP concentration in the pore water (PORE-water) at depth of 0-30 mm and reduced the concentration of PORE-water NH3-N at depth of 0-50 mm. Moreover, the Fe-CZ capping layer gave rise to the great decrement of the concentration of the labile P measured by DGT (diffusive gradient in thin films) technology (P-DGT) in the profile of OVER-water and sediment. Additionally, the Fe-CZ capping resulted in the reduction of redox-sensitive P (P-BD) in the 0-50 mm sediment and caused the transformation of P-BD to calcium-bound P (P-HCl) and residual P (P-RES) in the 0-10 mm sediment as well as to P-RES in the 10-20 mm sediment. Results of this work indicate that the Fe-CZ capping has a high potential for the simultaneous management of P and N release from sediments, and the decrease of the contents of sediment P-DGT, sediment P-BD, PORE-water SRP and PORE-water NH3-N as well as the conversion of mobile P to more stable P in the top sediment should have a significant role in the simultaneous interception of sedimentary P and N liberation into OVER-water by the Fe-CZ capping.

Low-cost cultivation and sporulation of alkaliphilic Bacillus sp. strain AK13 for self-healing concrete.

The alkaliphilic, calcium carbonate precipitating Bacillus sp. strain AK13 can be utilized in concrete for self-repairing. A statistical experimental design was used to develop an economical medium for its mass cultivation and sporulation. Two types of screening experiment were first conducted to identify substrates that promote the growth of the AK13 strain: the first followed a one-factor-at-a-time factorial design and the second a two-level full factorial design. Based on these screening experiments, barley malt powder and mixed grain powder were identified as the substrates that most effectively promoted the growth of the AK13 strain from a range of 21 agricultural products and by-products. A quadratic statistical model was then constructed using a central composite design and the concentration of the two substrates was optimized. The estimated growth and sporulation of Bacillus sp. strain AK13 in the proposed medium were 3.08 ± 0.38 × 108 and 1.25 ± 0.12 × 108 CFU/ml, respectively, which meant that the proposed low-cost medium was approximately 45 times more effective than the commercial medium in terms of the number of cultivatable bacteria per unit price. The spores were then powdered via a spray-drying process to produce a spore powder with a spore count of 2.0 ± 0.7 × 109 CFU/g. The AK13 spore powder was mixed with cement paste, yeast extract, calcium lactate, and water. The yeast extract and calcium lactate generated the highest CFU/ml for AK13 at a 0.4:0.4 ratio compared to 0.4:0.25 (the original ratio of the B4 medium) and 0.4:0.8. Twenty-eight days after the spores were mixed into the mortar, the number of vegetative cells and spores of the AK13 strain had reached 106 CFU/g within the mortar. Cracks in the mortar under 0.29 mm were healed in 14 days. Calcium carbonate precipitation was observed on the crack surface. The mortar containing the spore powder was thus concluded to be effective in terms of healing micro-cracks.

Towards a low CO2 emission building material employing bacterial metabolism (2/2): Prospects for global warming potential reduction in the concrete industry.

The production of concrete is one of the most significant contributors to global greenhouse gas emissions. This work focuses on bio-cementation-based products and their potential to reduce global warming potential (GWP). In particular, we address a proposed bio-cementation method employing bacterial metabolism in a two-step process of limestone dissolution and recrystallisation (BioZEment). A scenario-based techno-economic analysis (TEA) is combined with a life cycle assessment (LCA), a market model and a literature review of consumers' willingness to pay, to compute the expected reduction of global GWP. Based on the LCA, the GWP of 1 ton of BioZEment is found to be 70-83% lower than conventional concrete. In the TEA, three scenarios are investigated: brick, precast and onsite production. The results indicate that brick production may be the easiest way to implement the products, but that due to high cost, the impact on global GWP will be marginal. For precast production the expected 10% higher material cost of BioZEment only produces a marginal increase in total cost. Thus, precast production has the potential to reduce global GWP from concrete production by 0-20%. Significant technological hurdles remain before BioZEment-based products can be used in onsite construction scenarios, but in this scenario, the potential GWP reduction ranges from 1 to 26%. While the potential to reduce global GWP is substantial, significant efforts need to be made both in regard to public acceptance and production methods for this potential to be unlocked.

Potential of the Bioinspired CaCO3 Microspheres Loaded with Tetracycline in Inducing Differential Cytotoxic Effects toward Noncancerous and Cancer Cells: A Cytogenetic Toxicity Assessment Using CHO Cells in Vitro.

Calcium carbonate (CaCO3)-based materials as feasible pH-sensitive drug carriers, which can actively dissolve in an acidic microenvironment of cancer cells, are finding increasing importance. This has drawn our interest in the development of a bioinspired polypeptide- mediated method to design calcium carbonate microspheres loaded with tetracycline (CaCO3-TC) with an aim to explore its safe application in cancer therapeutics. Its therapeutic application in cancer patients essentially demands its safety information on the normal cells. Herein our study presents the in vitro genetic toxicological information on CaCO3-TC using noncancerous mammalian CHO cells in comparison to bare TC at three different concentrations (100, 200, and 300 µM) selected based on the cytotoxicity data (MTT). Assessment of various end points like chromosome aberrations, micronucleus, mitotic index and effects on cell cycle distribution after 24 h post-treatment demonstrates a significant reduction in clastogenic ( P < 0.001), aneugenic potential ( P < 0.05), and nonmitotoxic nature of CaCO3-TC than that of bare TC. Noticeably, as inferred from the FACS analysis on cancer cells, G2/M phase accumulation in breast cancer cells (MDA-MB-231), and at G1 phase in cervical cancer cells (HeLa) reveal its potential anticancer property. On the other hand, the genotoxicity studies illustrate protective effects of CaCO3-TC on noncancerous cells. While the pH-dependent dissolution property of the CaCO3 matrix encasing tetracycline results in higher toxicity on cancer cells, the near neutral pH in the case of normal cells prevents complete dissolution of CaCO3 thereby not allowing the encapsulated TC to adequately interact with the cells. Therefore, thus assembled CaCO3 spheres not only provide a way for facile encapsulation of tetracycline under mild conditions but also result in an effective matrix for differential toxicity toward normal and cancer cells justifying its clinical development as a novel target-specific drug in therapeutic applications for metastatic cancers.

RADIOACTIVITY MEASUREMENT AND RADIOLOGICAL HAZARD ASSESSMENT OF THE COMMONLY USED GRANITE AND MARBLE IN JORDAN.

Natural radioactivity of common commercial marble and granite types used in Jordanian dwellings are measured using high-resolution gamma spectrometry. The activity concentrations of 226Ra, 232Th and 40K ranged from 8.57 ± 1.55 to 152.07 ± 3.26 Bq kg-1, 6.83 ± 1.25 to 365.43 ± 4.84 Bq kg-1 and 121.25 ± 9.10 to 1604.90 ± 31.28 Bq kg-1 in granite and from 0.53 ± 0.12 to 18.61 ± 1.60 Bq kg-1, 0.51 ± 0.19 to 4.87 ± 2.13 Bq kg-1 and 3.21 ± 0.96 to 58.09 ± 6.40 Bq kg-1 in marble, respectively. Various radiological hazard indices like gamma index, internal and external hazard indices and annual effective dose equivalent were calculated and compared with the international limits. Our results show that some granite types may pose a radiation hazard.

Assessment of synergistic effect of combining hyperthermia with irradiation and calcium carbonate nanoparticles on proliferation of human breast adenocarcinoma cell line (MCF-7 cells).

The present study was undertaken to evaluate the synergistic effect of combining hyperthermia with irradiation and calcium carbonate nanoparticles (CC NPs) on proliferation of MCF-7 cells. The cells were randomly allocated to 19 groups: one negative control, three positive controls and 15 treatment groups. MCF-7 cells were treated with three concentrations of CC NPs (50, 100 and 150 µg/mL), gamma radiation (200 cGy), hyperthermia (41 °C for 1 h) and three concentrations of doxorubicin (200, 400 and 800 nm) and incubated at 37 °C for 24 h. Then the cell viability, the percentage of apoptosis and the levels of caspase-3, -8 and -9 proteins were measured. The results indicated that the combination group (150 µg/mL CC NPs + thermoradiotherapy) had a significant (p < .001) decrease in cell viability (48.65 ± 4.8%) and a significant (p < .001) increase in apoptosis percentage (45 ± 1.63%) of MCF-7 cells, as compared with the negative control and most of the other treatment groups. Moreover, a significant (p < .05) increase was observed in the activity of caspase-3 and caspase-9. Our findings revealed that CC NPs in combination with irradiation and hyperthermia could significantly reduce the cell viability and enhance the apoptosis of the MCF-7 breast cancer cells, the same as doxorubicin anti-cancer drug.

Performance assessment of laboratory and field-scale multi-step passive treatment of iron-rich acid mine drainage for design improvement.

Multi-step passive systems for the treatment of iron-rich acid mine drainage (Fe-rich AMD) perform satisfactorily at the laboratory scale. However, their field-scale application has revealed dissimilarities in performance, particularly with respect to hydraulic parameters. In this study, the assessment of factors potentially responsible for the variations in performance of laboratory and field-scale multi-step systems was undertaken. Three laboratory multi-step treatment scenarios, involving a combination of dispersed alkaline substrate (DAS) units, anoxic dolomitic drains, and passive biochemical reactors (PBRs), were set up in 10.7-L columns. The field-scale treatment consisted of two PBRs separated by a wood ash (WA) reactor. The parameters identified as possibly influencing the performances of the laboratory and field-scale experiments were the following: AMD chemistry (electrical conductivity and Fe and SO42- concentrations), flow rate (Q), and saturated hydraulic conductivity (ksat). Based on these findings, the design of an efficient passive multi-step treatment system is suggested to consider the following: (1) Fe pretreatment, using materials with high ksat and low HRT. If a PBR is to be used, the Fe load should be < 26 g/m3 substrate/day (Fe < 200 mg/L) and SO42- < 110 g/m3 substrate/day; (2) PBR/DAS filled with a mixture with at least 20% of neutralizing agent; (3) include Q and ksat (> 10-3 cm/s) in the long-term prediction. Finally, mesocosm testing is strongly recommended prior to construction of full-scale systems for the treatment of Fe-rich AMD.

Environmental risk assessment of cobalt and manganese from industrial sources in an estuarine system.

A total of 74 samples of soil, sediment, industrial sludge, and surface water were collected in a Mediterranean estuarine system in order to assess the potential ecological impact of elevated concentrations of Co and Mn associated with a Terephthalic (PTA) and Isophthalic (PIPA) acids production plant. Samples were analyzed for elemental composition (37 elements), pH, redox potential, organic carbon, and CaCO3 content, and a group of 16 selected samples were additionally subjected to a Tessier sequential extraction. Co and Mn soil concentrations were significantly higher inside the industrial facility and around its perimeter than in background samples, and maximum dissolved Co and Mn concentrations were found in a creek near the plant's discharge point, reaching values 17,700 and 156 times higher than their respective background concentrations. The ecological risk was evaluated as a function of Co and Mn fractionation and bioavailability which were controlled by the environmental conditions generated by the advance of seawater into the estuarine system during high tide. Co appeared to precipitate near the river mouth due to the pH increase produced by the influence of seawater intrusion, reaching hazardous concentrations in sediments. In terms of their bioavailability and the corresponding risk assessment code, both Co and Mn present sediment concentrations that result in medium to high ecological risk whereas water concentrations of both elements reach values that more than double their corresponding Secondary Acute Values.

Evaluating water quality and ecotoxicology assessment techniques using data from a lead and zinc effected upland limestone catchment.

Point and diffuse sources associated with historical metal ore mining are major causes of metal pollution. The understanding of metal behaviour and fate has been improved by the integration of water chemistry, metal availability and toxicity. Efforts have been devoted to the development of efficient methods of assessing and managing the risk posed by metals to aquatic life and meeting national water quality standards. This study focuses on the evaluation of current water quality and ecotoxicology techniques for the metal assessment of an upland limestone catchment located within a historical metal (lead ore) mining area in northern England. Within this catchment, metal toxicity occurs at circumneutral pH (6.2-7.5). Environmental Quality Standards (EQSs) based on a simple single concentration approach like hardness based EQS (EQS-H) are more overprotective, and from sixteen sites monitored in this study more than twelve sites (>75%) failed the EQSs for Zn and Pb. By increasing the complexity of assessment tools (e.g. bioavailability-based (EQS-B) and WHAM-FTOX), less conservative limits were provided, decreasing the number of sites with predicted ecological risk to seven (44%). Thus, this research supports the use of bioavailability-based approaches and their applicability for future metal risk assessments.

Reduction dye in paint and construction chemicals wastewater by improved coagulation-flocculation process.

A coagulation-flocculation process was applied to wastewater of paint and construction chemicals producing factory in Turkey. Ferric chloride was used as coagulant and several natural based materials, namely limestone, pumice, sepiolite, bentonite and mussel shell were used as flocculant aids. The effects of dosage of flocculant aids on the pH, color and electrical conductivity of wastewater were studied. The experimental results showed that the treatment with all substances was very effective. The pHs of treated wastewater were obtained in the range of 5-7 without needing pH adjustment process. Fifteen Pt-Co color values were obtained on average, which is similar to pure water clarity. The amount of solute in the wastewater was evaluated by the electrical conductivity values. According to the results, under the optimum treatment conditions, chemical oxygen demands were determined. As a result of the work, the cost of chemicals for the wastewater treatment processes has been reduced by about 90%.

Multiple phases of mg-calcite in crustose coralline algae suggest caution for temperature proxy and ocean acidification assessment: lessons from the ultrastructure and biomineralization in Phymatolithon (Rhodophyta, Corallinales)1.

Magnesium content, strongly correlated with temperature, has been developed as a climate archive for the late Holocene without considering anatomical controls on Mg content. In this paper, we explore the ultrastructure and cellular scale Mg-content variations within four species of North Atlantic crust-forming Phymatolithon. The cell wall has radial grains of Mg-calcite, whereas the interfilament (middle lamella) has grains aligned parallel to the filament axis. The proportion of interfilament and cell wall carbonate varies by tissue and species. Three distinct primary phases of Mg-calcite were identified: interfilament Mg-calcite (mean 8.9 mol% MgCO3 ), perithallial cell walls Mg-calcite (mean 13.4 mol% MgCO3 ), and hypothallium Mg-calcite (mean 17.1 mol% MgCO3 ). Magnesium content for the bulk crust, an average of all phases present, showed a strongly correlated (R2  = 0.975) increase of 0.31 mol% MgCO3 per °C. Of concern for climate reconstructions is the potential for false warming signals from undetected postgrazing wound repair carbonate that is substantially enriched in Mg, unrelated to temperature. Within a single crust, Mg-content of component carbonates ranged from 8 to 20 mol% MgCO3 , representing theoretical thermodynamic stabilities from aragonite-equivalent to unstable higher-Mg-calcite. It is unlikely that existing current predictions of ocean acidification impact on coralline algae, based on saturation states calculated using average Mg contents, provide an environmentally relevant estimate.

Predicting crystal growth via a unified kinetic three-dimensional partition model.

Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into 'natural tiles' or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and l-cystine.

Toward a holistic environmental impact assessment of marble quarrying and processing: proposal of a novel easy-to-use IPAT-based method.

Marble is a natural dimension stone that is widely used in building due to its resistance and esthetic qualities. Unfortunately, some concerns have arisen regarding its production process because quarrying and processing activities demand significant amounts of energy and greatly affect the environment. Further, performing an environmental analysis of a production process such as that of marble requires the consideration of many environmental aspects (e.g., noise, vibrations, dust and waste production, energy consumption). Unfortunately, the current impact accounting tools do not seem to be capable of considering all of the major aspects of the (marble) production process that may affect the environment and thus cannot provide a comprehensive and concise assessment of all environmental aspects associated with the marble production process. Therefore, innovative, easy, and reliable methods for evaluating its environmental impact are necessary, and they must be accessible for the non-technician. The present study intends to provide a contribution in this sense by proposing a reliable and easy-to-use evaluation method to assess the significance of the environmental impacts associated with the marble production process. In addition, an application of the method to an actual marble-producing company is presented to demonstrate its practicability. Because of its relative ease of use, the method presented here can also be used as a "self-assessment" tool for pursuing a virtuous environmental policy because it enables company owners to easily identify the segments of their production chain that most require environmental enhancement.

Effects of elevated pCO2 and feeding on net calcification and energy budget of the Mediterranean cold-water coral Madrepora oculata.

Ocean acidification is a major threat to calcifying marine organisms such as deep-sea cold-water corals (CWCs), but related knowledge is scarce. The aragonite saturation threshold (Ωa) for calcification, respiration and organic matter fluxes were investigated experimentally in the Mediterranean Madrepora oculata Over 10 weeks, colonies were maintained under two feeding regimes (uptake of 36.75 and 7.46 µmol C polyp-1 week-1) and exposed in 2 week intervals to a consecutively changing air-CO2 mix (pCO2) of 400, 1600, 800, 2000 and 400 ppm. There was a significant effect of feeding on calcification at initial ambient pCO2, while with consecutive pCO2 treatments, feeding had no effect on calcification. Respiration was not significantly affected by feeding or pCO2 levels. Coral skeletons started to dissolve at an average Ωa threshold of 0.92, but recovered and started to calcify again at Ωa≥1. The surplus energy required to counteract dissolution at elevated pCO2 (≥1600 µatm) was twice that at ambient pCO2 Yet, feeding had no mitigating effect at increasing pCO2 levels. This could be due to the fact that the energy required for calcification is a small fraction (1-3%) of the total metabolic energy demand and corals even under low food conditions might therefore still be able to allocate this small portion of energy to calcification. The response and resistance to ocean acidification are consequently not controlled by feeding in this species, but more likely by chemical reactions at the site of calcification and exchange processes between the calicoblastic layer and ambient seawater.

Assessment of waste oyster shells and coal mine drainage sludge for the stabilization of As-, Pb-, and Cu-contaminated soil.

A novel treatment mix was designed for the simultaneous immobilization of As, Cu, and Pb in contaminated soils using natural (waste oyster shells (WOS)) and industrial (coal mine drainage sludge (CMDS)) waste materials. The treatments were conducted using the standard U.S. sieve size no. 20 (0.85 mm) calcined oyster shells (COS) and CMDS materials with a curing time of 1 and 28 days. The As immobilization treatments were evaluated using the 1-N HCl extraction fluid, whereas the Pb and Cu immobilization treatments were evaluated using the 0.1-N HCl extraction fluid based on the Korean leaching standards. The treatment results showed that the immobilization of As, Cu, and Pb was best achieved using a combination mix of 10 wt% COS and 10 wt% CMDS. This treatment mix was highly effective leading to superior leachability reductions for all three target contaminants (>93 % for As and >99 % for Cu and Pb) for a curing period of 28 days. The X-ray absorption near-edge structure (XANES) results showed that As was present in the form of As(V) in the control sample and that no changes in As speciation were observed following the COS-CMDS treatments. The scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) sample treated with 10 wt% COS and 10 wt% CMDS indicated that As immobilization may be associated with the formation of Ca-As and Fe-As precipitates while Pb and Cu immobilization was most probably linked to calcium silicate hydrates (CSHs) and calcium aluminum hydrates (CAHs).

Circular economy in drinking water treatment: reuse of ground pellets as seeding material in the pellet softening process.

Calcium carbonate pellets are produced as a by-product in the pellet softening process. In the Netherlands, these pellets are applied as a raw material in several industrial and agricultural processes. The sand grain inside the pellet hinders the application in some high-potential market segments such as paper and glass. Substitution of the sand grain with a calcite grain (100% calcium carbonate) is in principle possible, and could significantly improve the pellet quality. In this study, the grinding and sieving of pellets, and the subsequent reuse as seeding material in pellet softening were tested with two pilot reactors in parallel. In one reactor, garnet sand was used as seeding material, in the other ground calcite. Garnet sand and ground calcite performed equally well. An economic comparison and a life-cycle assessment were made as well. The results show that the reuse of ground calcite as seeding material in pellet softening is technologically possible, reduces the operational costs by €38,000 (1%) and reduces the environmental impact by 5%. Therefore, at the drinking water facility, Weesperkarspel of Waternet, the transition from garnet sand to ground calcite will be made at full scale, based on this pilot plant research.

Representative elementary volume assessment of three-dimensional x-ray microtomography images of heterogeneous materials: application to limestones.

Over the last 15 years, x-ray microtomography has become a useful technique to obtain morphological, structural, and topological information on materials. Moreover, these three-dimensional (3D) images can be used as input data to assess certain properties (e.g., permeability) or to simulate phenomena (e.g., transfer properties). In order to capture all the features of interest, high spatial resolution is required. This involves imaging small samples, raising the question of the representativity of the data sets. In this article, we (i) present a methodology to analyze the microstructural properties of complex porous media from 3D images, (ii) assess statistical representative elementary volumes (REVs) for such materials; and (iii) establish criteria to delimit these REVs. In the context of cultural heritage conservation, a statistical study was done on 30 quarry samples for three sorts of stones. We first present the principles of x-ray microtomography experiments and emphasize the care that must be taken in the 3D image segmentation steps. Results show that statistical REVs exist for these media and are reached for the image sizes studied (1300 × 1300 × 1000 voxels) for two characteristics: porosity and chord length distributions. Furthermore, the estimators used (porosity, autocorrelation function, and chord length distributions) are sufficiently sensitive to quantitatively distinguish these three porous media from each other. Lastly, this study puts forward criteria based on the above-mentioned estimators to evaluate the REVs. These criteria avoid having to repeat the statistical study for each new material studied. This is particularly relevant to quantitatively monitor the modifications in materials (weathering, deformation …) or to determine the smallest 3D volume for simulation in order to reduce computing time.