Precipitated CaCO3 Research Articles

Carbonic Anhydrase Immobilized on Encapsulated Magnetic Nanoparticles for CO2 Sequestration

Bovine carbonic anhydrase (BCA) was covalently immobilized onto OAPS (octa(aminophenyl)silsesquioxane)-functionalized Fe(3)O(4)/SiO(2) nanoparticles by using glutaraldehyde as a spacer. The Fe(3)O(4) nanoparticles were coated with SiO(2), onto which was grafted OAPS, and the product was characterized using SEM, TEM, XRD, IR, X-ray photoelectron spectroscopy (XPS), and magnetometer analysis. The enzymatic activities of the free and Fe(3)O(4)/SiO(2)/OAPS-conjugated BCA (Fe-CA) were investigated by hydrolyzing p-nitrophenylacetate (p-NPA), and hydration and sequestration of CO(2) to CaCO(3). The CO(2) conversion efficiency and reusability of the Fe-CA were studied before and after washing the recovered Fe-CA by applying a magnetic field and quantifying the unreacted Ca(2+) ions by using ion chromatography. After 30 cycles, the Fe-CA displayed strong activity, and the CO(2) capture efficiency was 26-fold higher than that of the free enzyme. Storage stability studies suggested that Fe-CA retained nearly 82 % of its activity after 30 days. Nucleation of the precipitated CaCO(3) was monitored by using polarized light microscopy, which revealed the formation of two phases, calcite and valerite, at pH 10 upon addition of serine. The magnetic nanobiocatalyst was shown to be an excellent reusable catalyst for the sequestration of CO(2).

Influence of NaCl on mineral carbonation of CO2 using cement material in aqueous solutions

The carbonation of cement materials in NaCl solution was evaluated at various NaCl concentrations (0–2.0M). Leaching and carbonation tests were conducted on slurry-mixed ordinary Portland cement (OPC) with NaCl solutions at a solid to liquid ratio of 50g/l in a Teflon reactor under ambient temperature and pressure conditions. After 24-h leaching, the pH of the slurry decreased with increasing NaCl concentration, whereas the Ca concentration slightly increased. The C–S–H content in the reacted samples after 24-h leaching increased in the presence of NaCl. After the carbonation tests, the CaCO3 content in the reacted samples increased by 7.5–18.4wt%, whereas the C–S–H content decreased by 7.1–33.0wt% in the NaCl solutions. The particle size of the precipitated CaCO3 appeared to be decreased as the NaCl concentration was increased to 1M, but increased as the NaCl concentration was further increased to 2M.

Specific surface area and particle size of calcium carbonate precipitated by carbon dioxide microbubbles

Previously, it was found that precipitating CaCO3 through the carbonation route by bubbling carbon dioxide using a microbubble generator (MBG), as opposed to a conventional bubble generator, reduces the acquisition time. However, the physical properties of the precipitated CaCO3 (polymorph:calcite) using MBG have not been clarified. The physical properties of CaCO3 determine its usefulness in diverse fields. Therefore, this study investigated the specific surface area and size of primary and secondary calcite particles obtained using MBG. These properties were found to be affected by the Ca(OH)2 concentration, CO2 injection rate, and electrolyte dose in the suspension supplying the calcium ions. Comparison with control experiments using a conventional bubble generator showed that the particles obtained using MBG are smaller and have a greater specific surface area. The fine calcite particles with large specific surface area obtained by the additive-less precipitation using MBG are expected to be applied to the removal of acidic gas, such as sulfur dioxide, and as a paper making filler. The low cost and high CO2 consumption efficiency afforded by the MBG also make it promising for carbon capture and utilization.

Involvement of Bacteria in the Origin of a Newly Described Speleothem in the Gypsum Cave of Grave Grubbo (Crotone, Italy)

Microorganisms have been shown to be important active and passive promoters of redox reactions that influence the precipitation of various minerals, including calcite. Many types of secondary minerals thought to be of purely inorganic origin are currently being reevaluated, and microbial involvement has been demonstrated in the formation of pool fingers, stalactites and stalagmites, cave pisoliths, and moonmilk. We studied the possible involvement of bacteria in the formation of a new type of speleothem from Grave Grubbo Cave, the third-largest gypsum cave in Italy. The speleothem we studied consisted of a large aggregate of calcite tubes having a complex morphology, reflecting its possible organic origin. We isolated an abundant heterotrophic microflora associated with this concretion and identified Bacillus, Burk- holderia ,a ndPasteurella spp. among the isolates. All of the isolates precipitated CaCO3 in vitro in the form of calcite. Only one of the isolates solubilized carbonate. The relative abundance of each isolate was found to be directly related to its ability to precipitate CaCO3 at cave temperature. We suggest that hypogean environments select for microbes exhibiting calcifying activity. Isotopic analysis produced speleothem d 13 C values of about - 5.00%, confirming its organic origin. The lightest carbonates purified from B4M agar plates were produced by the most abundant isolates. SEM analysis of the speleothem showed traces of calcified filamentous bacteria interacting with the substrate. Spherical bioliths predominated among the ones produced in vitro. Within the crystals produced in vitro, we observed bacterial imprints, sometimes in a preferred orientation, suggesting the involvement of a quorum-sensing system in the calcium-carbonate precipitation process.

Micronized CaCO3: a feasible alternative to limestone filtration for conditioning and (re)mineralization of drinking water?

Research Article| December 01 2011 Micronized CaCO3: a feasible alternative to limestone filtration for conditioning and (re)mineralization of drinking water? J. C. J. Gude; J. C. J. Gude 1Witteveen + Bos, PO Box 233, 7400 AE Deventer, The Netherlands Search for other works by this author on: This Site PubMed Google Scholar F. Schoonenberg Kegel; F. Schoonenberg Kegel 2Vitens, PO Box 1090, 8200 BB Lelystad, The Netherlands Search for other works by this author on: This Site PubMed Google Scholar W. J. C. van de Ven; W. J. C. van de Ven 2Vitens, PO Box 1090, 8200 BB Lelystad, The Netherlands Search for other works by this author on: This Site PubMed Google Scholar P. J. de Moel; P. J. de Moel 3Delft University of Technology, PO Box 5048, 2600 GA Delft, The Netherlands Search for other works by this author on: This Site PubMed Google Scholar J. Q. J. C. Verberk; J. Q. J. C. Verberk 3Delft University of Technology, PO Box 5048, 2600 GA Delft, The Netherlands E-mail: j.q.j.c.verberk@tudelft.nl Search for other works by this author on: This Site PubMed Google Scholar J. C. van Dijk J. C. van Dijk 3Delft University of Technology, PO Box 5048, 2600 GA Delft, The Netherlands Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2011) 60 (8): 469–477. https://doi.org/10.2166/aqua.2011.012 Article history Received: February 22 2011 Accepted: September 23 2011 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation J. C. J. Gude, F. Schoonenberg Kegel, W. J. C. van de Ven, P. J. de Moel, J. Q. J. C. Verberk, J. C. van Dijk; Micronized CaCO3: a feasible alternative to limestone filtration for conditioning and (re)mineralization of drinking water?. Journal of Water Supply: Research and Technology-Aqua 1 December 2011; 60 (8): 469–477. doi: https://doi.org/10.2166/aqua.2011.012 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Worldwide limestone filtration is used in many treatment plants for the conditioning and (re)mineralization of drinking water to increase concentrations of Ca2+ and HCO3−, pH and saturation index, thereby improving the quality of the water regarding corrosion control, buffering and taste. Typical applications include (very) soft groundwater with (very) low alkalinity and desalinated water. In Norway, some plants use a product made of ground natural limestone, called micronized CaCO3 slurry (MCCS), which is dosed as slurry of fine particles (1–2 μm) into the raw water. In this study the potential of MCCS as an alternative to limestone filtration was investigated. Experiments were performed to determine the dissolution kinetics of MCCS and other CaCO3-products, including natural limestone grains and two precipitated CaCO3 powders. As expected from theory, the dissolution kinetics are strongly influenced by the particle size of the CaCO3 and the driving force towards the chemical equilibrium. However, all CaCO3-products needed substantial detention times (30 min and more) to dissolve completely. It is concluded that MCCS is generally not a feasible alternative for limestone filtration as a stand-alone option for the conditioning and (re)mineralization of drinking water. Applications of MCCS are limited and should either be found in combinations with coagulation/filtration or with other conditioning and (re)mineralization methods. conditioning, dissolution kinetics, limestone filtration, micronized CaCO3, (re)mineralization This content is only available as a PDF. © IWA Publishing 2011 You do not currently have access to this content.

Calcium carbonate precipitation by anoxygenic phototrophic bacteria

Carbonate biomineralization is considered as one of the main natural processes controlling CO 2 levels in the atmosphere both in the past and at present time. In contrast to extensive studies of cyanobacterial calcification, biomineralization of anoxygenic phototrophic bacteria (APB) remained largely underestimated, despite their potentially important role on CaCO 3 precipitation in the biomats, notably in the past. Haloalcaliphilic Rhodovulum steppense A-20s and halophilic neutrophilic Rhodovulum sp. S-17-65 were examined with respect to their ability to precipitate CaCO 3 under controlled laboratory conditions. To characterize the link between the rate of bacterial growth (biomass production) and the rate of CaCO 3 precipitation, batch kinetic experiments with live, dead and inactivated bacteria both in nutrient solution and in inert electrolyte were performed and produced precipitates were examined by SEM, TEM and XRD techniques. Active strains A-20s and S-17-65 precipitated calcite from initially supersaturated solutions ( Ω calcite = 10 to 40) via increasing Ω calcite to 80–120 before the precipitation. The amount of precipitated CaCO 3 (mole) was directly correlated with the amount of organic C in bacterial biomass produced with a slope of dependence ranging from 0.3 to 0.6 and from 0.1 to 0.3 for A-20s and S-17-65, respectively, depending on the initial solution composition. For both bacterial strains, only live actively photosynthetizing bacteria were capable of effectively decreasing Ca concentration and form CaCO 3 with apparent bulk precipitation rates ranging from 0.001 to 0.0150 mmol/h at 10–20 g wet/L of biomass, similar to rates reported for other bacteria. SEM and XRD analyses of precipitates reveal the dominance of calcite with some amount of vaterite and monohydrocalcite forming spheres up to 100 μm diameter. The TEM analysis of bacterial suspension at the end of precipitation experiments did not demonstrate the presence of CaCO 3 at the surface or in the vicinity of live cells. This suggests the existence of certain cell protection mechanism against carbonate precipitation at the cell surface. Given the lower efficiency of photoheterotrophic APB, compared to photoautotrophic cyanobacteria, to precipitate CaCO 3 in natural conditions, it is possible that the overall potential of phototrophic community to form massive carbonate deposits was strongly limited before the appearance of oxygenic phototrophs.

Sand bioconsolidation through the precipitation of calcium carbonate by two ureolytic bacteria

Two ureolytic strains, B. sphaericus LMG 22257 and Bacillus sp (I-001), were tested for their ability to consolidate sand by submitting them to two days' treatment using 10 7 viable cell concentrations of inocula and medium precipitation with calcium ions. The results showed that B. sphaericus LMG 22257 induced greater calcium carbonate formation. Both strains produced calcite and were able to consolidate sand. Tensile strength of consolidated sand was not a function of the amount of precipitated CaCO 3 but a linear function of the ratio bioconsolidation index (BC) defined as the ratio of CaCO 3 volume to initial sand porosity. A simple model to estimate the engineering benefits of consolidation is proposed.

Effects of long-term use of sodic water irrigation, amendments and crop residues on soil properties and crop yields in rice–wheat cropping system in a calcareous soil

One of the options to ameliorate the deleterious effects of sodic water irrigation is to apply gypsum to soil. We examined whether the application of organic manures or crop residue can reduce the need for gypsum in calcareous soils. A long-term field experiment with annual rice–wheat cropping rotation was conducted for 15 years (1991–2006) on a non-saline calcareous sandy loam soil ( Typic Ustochrept) in northwestern, India. The irrigation water treatments included good quality canal water (CW) and sodic water (SW) with residual sodium carbonate (RSC) of 10 mmol c L −1 from 1991 to 1999 and of 12.5 mmol c L −1 from 2000 onwards. Gypsum was applied at 0, 12.5, 25, and 50% of the gypsum requirement (GR), to neutralize RSC of the SW. Three organic material treatments consisted of application of farmyard manure (FYM) at 20 Mg ha −1, Sesbania green manure (GM) at 20 Mg ha −1, and wheat straw (WS) at 6 Mg ha −1. The organic materials were applied every year to the rice crop. Continuous irrigation with sodic water for 15 years without gypsum or organic materials resulted in a gradual increase in soil pH and exchangeable sodium percentage (ESP), deterioration of soil physical properties, and decrease in yields of both rice and wheat. The cumulative yield loss in SW irrigated plots without gypsum and organic materials remained <1.5 Mg ha −1 for up to eight years in the case of rice and up to nine years in the case of wheat. Thereafter, marked increase in pH and ESP resulted in further depression in yields of rice by 1.6 Mg ha −1 year −1 and wheat by 1.2 Mg ha −1 year −1. Application of gypsum improved physical and chemical properties of the soil. The beneficial effects on crop yields were visible up to 12.5% GR in rice and up to 50% GR in wheat in most of the years. All the organic materials proved effective in mobilizing Ca 2+ from inherent and precipitated CaCO 3 resulting in decline in soil pH and ESP, increase in infiltration rate, and a increase in the yields of rice and wheat crops. Although the application of organic materials resulted in comparable reductions in pH and ESP, the increase in yield with SW was higher for both crops with FYM. Pooled over the last six years (2000–2006), application of FYM resulted in 38 and 26% increase in rice and wheat yields, respectively, over SW treatment; corresponding increases in 50% GR treatment (recommended level) was 18 and 19%. During these years, application of GM and WS increased wheat yields by 20%; for rice, GM resulted in 22% increase compared to 17% in WS amended SW irrigated plots. Combined application of gypsum and organic materials did not increase the yields further particularly in the case of FYM and GM treated plots. This long-term study proves that organic materials alone can be used to solubilize Ca from inherent and precipitated CaCO 3 in calcareous soils for achieving sustainable yields in sodic water irrigated rice–wheat grown in annual rotation. The results can help reduce the dependency on gypsum in sodic water irrigated calcareous soils.

Spring-associated limestones of the Eastern Alps: overview of facies, deposystems, minerals, and biota

In the Eastern Alps, both fossil spring limestones and actively limestone-depositing springs are common. The geological context and a few radiometric age data of fossil spring-associated limestones (SAL) mentioned herein indicate that they accumulated subsequent to the Last Glacial Maximum in the Eastern Alps (24–21 ka BP). Prevalent facies of the SAL deposits, active and fossil, including phytoclastic tufa, microbialites s.l., springstone, and moss tufa form, or formed, from (a) waterfall/creek systems, (b) hillslope-paludal systems, (c) moss-tufa systems, and from (c) foreland-type systems. Precipitated minerals include calcite and, at springs of elevated Mg/Ca ratio, magnesian calcite and aragonite. In a few limestone-depositing, oxygen-deficient springs with dissolved Fe2+, downstream, iron oxide precipitates ahead of CaCO3 (mineralogical zonation). Biota associated with calcium-carbonate deposition include cyanobacteria, green micro-algae, macro-algae, and mosses. Calcium-carbonate precipitation may be speeded by biological mediation, but mineralogy and polymorphy of precipitated CaCO3 are not biotically controlled. In the Eastern Alps, SAL deposits in total range from 190 to 2,520 m a.s.l., corresponding to mean annual temperatures of 10°C to less than 0°C. In altitudes below the continuous permafrost line (about 2,600–3,000 m a.s.l., depending on location), SAL deposition is chiefly controlled by proper balance between water supply and sufficient supersaturation for CaCO3, rather than by mean annual temperature.

PENGARUH MEDAN MAGNET TERHADAP PROSES PRESIPITASI CaCO3 DALAM AIR SADAH

Magnetic Field Effects on CaCO3 Precipitation Process in Hard Water. Magnetic treatment is applied as physical water treatment for scale prevention especially CaCO3, from hard water in piping equipment by reducing its hardness. Na2CO3 and CaCl2 solution sample was used in to investigate the magnetic fields influence on the formation of particle of CaCO3. By changing the strength of magnetic fields, exposure time and concentration of samples solution, this study presents quantitative results of total scale deposit, total precipitated CaCO3 and morphology of the deposit. This research was run by comparing magnetically and non-magnetically treated samples. The results showed an increase of deposits formation rate and total number of precipitated CaCO3 of magnetically treated samples. The increase of concentration solution sample will also raised the deposit under magnetic field. Microscope images showed a greater number but smaller size of CaCO3 deposits form in magnetically treated samples, and aggregation during the processes. X-ray diffraction (XRD) analysis showed that magnetically samples were dominated by calcite. But, there was a significant decrease of calcite’s peak intensities from magnetized samples that indicated the decrease of the amount of calcite and an increase of total amorphous of deposits. This result showed that magnetization of hard water leaded to the decreasing of ion Ca2+ due to the increasing of total CaCO3 precipitation process.

Bacterial Calcium Carbonate Precipitation in Cave Environments: A Function of Calcium Homeostasis

To determine if microbial species play an active role in the development of calcium carbonate (CaCO 3 ) deposits (speleothems) in cave environments, we isolated 51 culturable bacteria from a coralloid speleothem and tested their ability to dissolve and precipitate CaCO 3 . The majority of these isolates could precipitate CaCO 3 minerals; scanning electron microscopy and X-ray diffractrometry demonstrated that aragonite, calcite and vaterite were produced in this process. Due to the inability of dead cells to precipitate these minerals, this suggested that calcification requires metabolic activity. Given growth of these species on calcium acetate, but the toxicity of Ca 2+ ions to bacteria, we created a loss-of-function gene knock-out in the Ca 2+ ion efflux protein ChaA. The loss of this protein inhibited growth on media containing calcium, suggesting that the need to remove Ca 2+ ions from the cell may drive calcification. With no carbonate in the media used in the calcification studies, we used stable isotope probing with C 13 O 2 to determine whether atmospheric CO 2 could be the source of these ions. The resultant crystals were significantly enriched in this heavy isotope, suggesting that extracellular CO 2 does indeed contribute to the mineral structure. The physiological adaptation of removing toxic Ca 2+ ions by calcification, while useful in numerous environments, would be particularly beneficial to bacteria in Ca 2+ -rich cave environments. Such activity may also create the initial crystal nucleation sites that contribute to the formation of secondary CaCO 3 deposits within caves.

Use of bacteria to repair cracks in concrete

As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO 3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO 3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely.

A preliminary investigation into the use of acid-tolerant precipitated calcium carbonate fillers in papermaking of deinked pulp derived from recycled newspaper

The use of acid-tolerant precipitated calcium carbonate fillers, including phosphoric acid/sodium hexametaphosphate modified precipitated CaCO3 filler, and sodium silicate/phosphoric acid/sodium hexametaphos-phate modified precipitated CaCO3 filler in papermaking of deinked pulp derived from recycled newspaper was explored. These two acid-tolerant fillers provided considerably more brightness improvement in papers in comparison the unmodified filler, presumably indicating alleviated pulp darkening achieved as a result of better acid-resistant properties. The addition of acid-tolerant fillers into the furnish slurries gave lower system pH as compared with unmodified filler. Among the three fillers used in this work, the effect on retention of modification of the filler with sodium silicate/phosphoric acid/sodium hexametaphosphate was probably the best, as evaluated from ash content measurements. For air permeability of the paper, the use of acid-tolerant fillers provided slightly more improvement in comparison to the unmodified filler. For tensile and burst strength of the paper, the use of sodium silicate/phosphoric acid/sodium hexameta-phosphate modified precipitated calcium carbonate filler gave better results as compared with the other two fillers. Additionally, the improving effect of acid-tolerant fillers on furnish static drainage was found to be slightly weaker than that of unmodified filler.

Precipitation of nanostructured calcite in a controlled multiphase process

The way of conducting the precipitation process is crucial for the final product properties and its further applications. In the presented experiments, CaCO 3 powders were produced by controlled fast precipitation through gaseous CO 2 absorption in Ca(OH) 2 slurry. This multiphase reaction was conducted in a new rotating disc reactor unit, which enables one to control inter- and intra-face mass and energy transfer as well as the macro- and micro-mixing effects in the reacting system. The effect of calcium hydroxide concentration, mixing conditions in the reactor and gas–liquid interface development at discs surface on precipitated CaCO 3 was investigated. The analysis with the dynamic light scattering method (DLS) showed that mean particle diameter decreases with higher rate of discs revolution speed and higher calcium hydroxide concentration. The X-ray diffraction testing revealed that we have obtained a chemically pure calcite, which is the most stable polymorph of CaCO 3. The scanning electron micrographs (SEM) showed the influence of precipitation conditions on rhombohedral calcite crystals. Sorptometric surface analyses reveal high development of specific surface area (over 20 m 2g −1) and powders porosity.

Oxygenation of the ocean and sediments: Consequences for the seafloor carbonate factory

Observed changes in the source of CaCO 3 sediments since Archean time suggest a first order pattern of decreasing abundance of carbonate cements precipitated directly on the seafloor. We propose that the observed reduction in CaCO 3 precipitation on the seafloor is caused by a decrease in CaCO 3 saturation in sediments related to increased oxic cycling of organic carbon and a decline in the size of the marine DIC reservoir. Using a simple model of CaCO 3 saturation in the ocean, we show that changes in ocean–atmosphere redox and the size of the marine carbon reservoir strongly influence the ability of sediments to dissolve or precipitate CaCO 3. Oxic oceans like the modern are characterized by large gradients in CaCO 3 saturation. Calcium carbonate precipitates where CaCO 3 saturation is high (surface ocean) and dissolves where CaCO 3 saturation is low (sediments). In contrast, anoxic respiration of organic carbon and/or a large ocean carbon reservoir leads to a more homogeneous distribution of CaCO 3 saturation in the ocean and sediments. This effect suppresses CaCO 3 dissolution and promotes CaCO 3 precipitation on the seafloor. Our results suggest that the growth or contraction of gradients in CaCO 3 saturation in the ocean and sediments may explain the observed trends in carbonate precipitation on the seafloor in the Precambrian and changes in the global CaCO 3 cycle, such as the reappearance of seafloor precipitates and the drowning of carbonate platforms during episodes of widespread anoxia in the Phanerozoic marine basins. Our work provides novel insights into the consequences of the long-term geochemical evolution of the ocean and atmosphere for the global CaCO 3 cycle.

Modeling the effect of anti-scalant on CaCO3 precipitation in continuous flow

Scale inhibition by anti-scalants is known to involve blockage of active growth sites by adsorbed inhibitor molecules, but there is virtually no quantitative information on the kinetics of anti-scalant retarded precipitation. This paper presents a model integrating the process of anti-scalant adsorption on precipitated CaCO3 particles with the kinetics of the ensuing retarded precipitation. Adsorption is analyzed according to the Langmuir, Freundlich and Langmuir-Freundlich models, and CaCO3 precipitation is described by the commonly used surface reaction controlled model. The proposed model is validated by experimental data measured in a continuous flow precipitation system over a wide range of conditions.

Development of the electrochemical scale removal technique for desalination applications

The possibility of alkaline scale precipitation and removal by electrolytic devices has long been recognized. The scale removal principle of the electrochemical technique is based on the creation of a high pH environment around the cathode by water and oxygen reduction reactions which release hydroxyl ions. The alkaline environment induces precipitation of the calcium hardness in the form of CaCO 3 and of the magnesium hardness, in the form of Mg(OH) 2. Despite the commercial availability of such equipment, the use of electrochemical scale control methods is quite limited. Currently, the main field of application of electrolytic devices is for reducing the hardness of water recirculating in cooling towers. The lack of authoritative technical information on electrochemical scale removal reflects the paucity of research and development efforts in a technology which holds considerable promise for expanding the rather limited scope of viable scale control techniques. The objectives of this research project are to evaluate the potential of the electrochemical technique for RO desalination processes in general and for increasing water recovery levels in particular. The paper summarizes results of the first phase of the research. Models describing cell resistance in the absence and in the presence of a deposit on the cathode are presented. The effects of several parameters on the deposition rate and on the electric energy consumption are investigated. Results show that the higher the water hardness, the higher the scale precipitation rate and the lower the specific energy consumption. An increase in the flow velocity augments the scale deposition rate. Analysis of the velocity effect data indicates that the scale precipitation reaction is mass transfer controlled. The main optimization parameter is the current density. As may be anticipated, a low specific electrical energy is consumed when the electrolyzed solution is exposed to a large electrode surface and a high specific energy is consumed when the solution is exposed to a small electrode surface. The energy consumption can be rather low. For instance, in the electrolysis of a typical concentrate stream of a brackish desalination plant at a current density of 25 A/m 2, the energy consumption is of the order of 4 kWh per kg of precipitated CaCO 3 and the scale precipitation rate is of the order of 25 g CaCO 3/h m 2. Finally, a flow scheme is presented indicating the possibility of beneficial increase of the water recovery level in brackish water RO desalination, by partial recycle of the concentrate after electrochemical precipitation of the scale forming ions held in solution by the anti-scalant.

Removal of CaCO3 Scaling Salt from RO Concentrates by Air-Blow and Inorganic Inducers

The reuse of reverse osmosis (RO) concentrates generally involves the removal of scaling salts such as CaSO4/CaCO3, and then the recycle part of the treated concentrate to the feed. By this method, the water recovery can be remarkably increased. However, the time necessary for precipitating the scaling components may extend to a few days, especially in the presence of antiscalants. In the present study, CaCO3 scaling salt removal was carried out from RO concentrates in the presence of three antiscalants by accelerating precipitation approaches. Three methods were adopted, including the air-blow method, inorganic inducer addition, and the combinative method of air-blow and inorganic inducer addition. Calcium ion concentration, pH and antiscalant concentration of the test solutions were monitored. Morphologies of the precipitated CaCO3 were observed by scanning electron microscopy (SEM). These methods were found to be effective, reaching a calcium removal ratio as high as 50–80%. The removal of scaling salt was always accompanied by the adsorption precipitation of antiscalants. In the presence of antiscalants, saw-toothed growth edges and holes on the precipitated CaCO3 surfaces were found. Moreover, fragmented small particles were also observed. The economic analysis shows that the methods are feasible.

The development of nanoparticulate materials for biodegradable bone fracture plates: (I)

A cost effective route for the production of nanoparticulate calcium carbonate with high phase purity, a narrow particle size range and low tendency for agglomeration represents a crucial stage in the development of degradable nanocomposite materials for the manufacture of fracture fixation plates. In this study, the size, morphology and zeta potential of calcium carbonate (CaCO3) precipitated through carbonation of an aqueous solution of calcium hydroxide were investigated experimentally. It was found that the precipitating temperature, pH and the addition of a chelating agent were most influential in producing nanoparticulate CaCO3. The smallest particles (mean of 48 nm) were produced with an initial temperature of −93°C, initial pH of 8.5 and EDTA added. This route also has the advantage of narrow particle size distributions, which together with a zeta potential greater than 30 mV means that the precipitated CaCO3 is well suited for use as a filler in a biodegradable nanocomposite as indicated above.

Effect of sodium polyacrylate molecular weight on the crystallogenesis of calcium carbonate

Aqueous solutions of sodium polyacrylates (NaPA) series having molecular weights ( M w) ranging from 2540 to 9890 g mol −1 are used as precipitation media to control the size and shape of calcium carbonate (CaCO 3) particles. The retarding effect of polyacrylates on CaCO 3 nucleation is evidenced by the increase of the induction time, τ, of the precipitated CaCO 3, from τ=55 s in the absence of additives, to τ values in the range 100–2500 s in the presence of NaPA samples. The data also show the coexistence of two polymorphs, calcite and vaterite, for CaCO 3 particles as prepared in the presence of NaPA samples. The vaterite fraction, f v, varies in all instances with the polymer concentration, Cpoly (g. L −1), and reaches its maximum value, f v,max at optimal ratio, R (mol. g −1), of Ca ion to polymer (NaPA), R=[Ca]/([NaPA]=Cpoly). No simple general trend is found to explain the influence of the molecular weight ( M w) of NaPA on the induction time, τ, and on the vaterite fraction, f v, since these two parameters are found to vary with Cpoly and M w. However, under certain experimental conditions, an optimum polymer molecular weight ( M w=5530 g mol −1) of the NaPA series, gives the highest values of f v,max and τ. Such optimum indicates the influence of M w of NaPA on CaCO 3 nucleation and growth, and it is related to the surface density and the rate of adsorption of the polymer onto the growing crystal. The CaCO 3 particle size is reduced from about 20 μm, as obtained in the control experiment, to sizes varying in the range 2–8 μm in the presence NaPA samples. Polymers having low M w values ( M w<5000 g mol −1) are found to be more efficient in reducing the CaCO 3 particle size.