CaCO3 Loading Research Articles

Thermal and mechanical properties of modified CaCO3 filled poly (ethylene terephthalate) nanocomposites

Poly(ethylene terephthalate) (PET)/CaCO3 and PET/modified-CaCO3 (m-CaCO3) nanocomposites were prepared by melt blending. The morphology indicated that m-CaCO3 produced by reacting sodium oxalate and calcium chloride, was well dispersed in PET matrix and showed good interfacial interaction with PET compared to CaCO3. No significant differences in the thermal properties such as, glass transition, melting and degradation temperatures, of the nanocomposites were observed. The thermal shrinkage of PET at 120 °C was 10.8 %, while those of PET/CaCO3 and PET/m-CaCO3 nanocomposites were 2.9–5.2 % and 1.2–2.8 %, respectively depending on filler content. The tensile strength of PET/CaCO3 nanocomposite decreased with CaCO3 loading, whereas that of PET/m-CaCO3 nanocomposites at 0.5 wt% loading showed a 17 % improvement as compared to neat PET. The storage modulus at 120 °C increased from 1660 MPa for PET to 2350 MPa for PET/CaCO3 nanocomposite at 3 wt% loading, and 3230 MPa for PET/m-CaCO3 nanocomposite at 1 wt% loading.

Modelling and optimization of rebound resilience and hardness of defatted rice bran/calcium carbonate-filled NR vulcanisates

Hardness and rebound resilience of natural rubber (NR) vulcanisates filled with defatted rice bran (DRB)/calcium carbonate (CaCO3) were modelled and optimized. Second-order polynomial functions were generated to model the properties and to generate contour plots. Predicted properties of NR vulcanisates showed good agreement with experimental results. Hardness of filled-NR vulcanisates increased with filler loading, whereas rebound resilience decreased. At a fixed hardness level, lower CaCO3 loading can be used with partial DRB replacement. DRB incorporation into rubber compounds can improve their stiffness. Contour plots were used to identify DRB and CaCO3 level ranges for achieving optimum hardness and rebound resilience.

EFFECTS OF PARTIAL REPLACEMENT OF RATTAN POWDER BY COMMERCIAL FILLERS ON THE PROPERTIES OF NATURAL RUBBER COMPOSITES

The effects of partial replacement of rattan powder (RP) by carbon black (CB), mica, and calcium carbonate (CaCO3) on the curing characteristics, tensile properties, rubber-filler interaction, and morphological studies of natural rubber (NR) composites were investigated. Rattan powder with an average particle size of less than 180 µm was used in this study. NR/RP/CB, NR/RP/mica, and NR/RP/CaCO3 composites with five different RP/commercial fillers loadings (i.e. 30/0, 20/10, 15/15, 10/20, 0/30 phr) were prepared using a laboratory size two-roll mill. Results showed that the maximum torque (MH) of the NR/RP/CB, NR/RP/mica, and NR/RP/CaCO3 composites increased with increasing the commercial filler-loading ratio. The scorch time (ts2) and cure time (t90) of NR/RP/CB composites decreased as the ratio of CB loading was increased, whereas, ts2 and t90 of NR/RP/mica and NR/RP/CaCO3 composites increased as mica and CaCO3 loading ratio were raised, respectively. The tensile strength, elongation at break (Eb), stress at 100% elongation (M100), and stress at 300% elongation (M300) of all the composites increased as the commercial filler-loading ratio increased. This is due to the presence of the commercial filler, which brought a better rubber-filler interaction, as confirmed by the rubber-filler interaction and scanning electron microscopy (SEM) studies.

Atomic Force Microscopy, thermal, viscoelastic and mechanical properties of HDPE/CaCO3 nanocomposites

High Density Polyethylene (HDPE) and calcium carbonate (CaCO3) nanocomposites were prepared from masterbatch by melt blending in twin screw extruder (TSE). The physical properties of HDPE/CaCO3 nanocomposites samples (0, 10 and 20 wt% CaCO3 masterbatch) were investigated. The morphology, thermal, rheological/viscoelastic and mechanical properties of the nanocomposites were characterized by Atomic Force microscopy (AFM), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analyzer (DMA) as well as tensile test. The AFM images showed homogeneous dispersion and distribution of nano-CaCO3 in the HDPE matrix. The DSC analysis showed a decrease in crystallinity of HDPE/CaCO3 nanocomposites with the increase of CaCO3 loading. This was due to the presence of nanofiller which could restrict the movement of the polymer chain segments and reduced the free volume/spaces available to be occupied by the macromolecules, thus, hindered the crystal growth. However, there was an increase in crystallization temperature about 1–2 °C with the addition of CaCO3. It was suggested that the CaCO3 nanoparticles acted as nucleating agent. In melt rheology study, the complex viscosities of HDPE/CaCO3 nanocomposites were higher than the HDPE matrix and increased with the increasing of CaCO3 masterbatch loading. The DMA results showed that the storage modulus increased with the increasing of nano-CaCO3 contents. The improvement was more than 40 %, as compared to that of neat HDPE. Additionally, the tensile test results showed that with the addition of CaCO3 masterbatch, modulus elasticity of nanocomposites sample increased while yield stress decreased.

Processing–Structure–Property Correlations of Polyethersulfone/Perfluorosulfonic Acid Nanofibers Fabricated via Electrospinning from Polymer–Nanoparticle Suspensions

Polyethersulfone (PES)/perfluorosulfonic acid (PFSA) nanofiber membranes were successfully fabricated via electrospinning method from polymer solutions containing dispersed calcium carbonate (CaCO(3)) nanoparticles. ATR-FTIR spectra indicated that the nanoparticles mainly existed on the external surface of the nanofibers and could be removed completely by acid treatment. Surface roughness of both the nanofibers and the nanofiber membranes increased with the CaCO(3) loading. Although FTIR spectra showed no special interaction between sulfonic acid (-SO(3)) groups and CaCO(3) nanoparticles, XPS measurement demonstrated that the content of -SO(3) groups on external surface of the acid-treated nanofibers was enhanced by increasing CaCO(3) loading in solution. Besides, the acid-treated nanofiber membranes were performed in esterification reactions, and exhibited acceptable catalytic performance due to the activity of -SO(3)H groups on the nanofiber surface. More importantly, this type of membrane was very easy to separate and recover, which made it a potential substitution for traditional liquid acid catalysts.

聚乳酸与碳酸钙复合物的制备及碳酸钙的降解抑制作用<br>Preparation of the PLA/CaCO3 Composites and the Retardation Effect of the CaCO3 on the Hydrolytic Degradation of the PLA in the Composites

采用熔融共混法，将聚乳酸(PLA)与碳酸钙(CaCO3)(2%、5%和7%)复合制备聚乳酸/碳酸钙复合物。通过复合物和纯PLA在磷酸盐缓冲溶液中浸泡后，不同碳酸钙含量的复合物复合前后PLA发生粘度变化，研究CaCO3对PLA/CaCO3复合物中PLA降解的抑制作用，并提出抑制机理。PLA/CaCO3复合物的力学性能和耐水性能的结果表明，添加一定量CaCO3的复合材料的拉伸强度、断裂伸长率、弹性模量和最大负荷明显增强。通过吸水率的测定，表明吸水率值随着CaCO3含量(2%和5%)的不同变化不大，而当含量增加到7%时，吸水率增大较多。随着吸水实验介质的不同，在磷酸盐缓冲溶液中浸泡的吸水率略高于在蒸馏水中浸泡的吸水率。 The poly (lactic acid) (PLA)/CaCO3 composites were prepared via melt blending in an intensive mixer of the torque rheometer. Hydrolytic degradation of the composites obtained was investigated comparatively with the pure PLA matrix. The hydrolytic degradation was carried out by immersing the film samples in phosphate buffer saline (pH = 7.4) at 37˚C, and the viscosity of the PLA in the degraded films was measured. The results indicated that the hydrolytic degradation of the PLA matrix in the composites was retarded as a result of the incorporation of the basic CaCO3 which would react with the partial end-carboxyl groups of the PLA matrix. It was showed that the tensile strength, elastic modulus, elongation at break and maximum load of the composites were enhanced significantly. Also it was found that the water absorption of the PLA/CaCO3 composites at low CaCO3 loading (2% and 5%) slightly increased compared with the pure PLA upon immersion for 4 weeks, while the PLA/CaCO3-7 composite had a much higher water absorption (5.5% - 6.0%) than the pure PLA in two immersion mediums. All composites exhibited slightly higher water resistance in the distilled water than in the phosphate buffer solution at pH = 7.4.

聚乳酸与碳酸钙复合物的制备及碳酸钙的降解抑制作用

采用熔融共混法，将聚乳酸(PLA)与碳酸钙(CaCO3)(2%、5%和7%)复合制备聚乳酸/碳酸钙复合物。通过复合物和纯PLA在磷酸盐缓冲溶液中浸泡后，不同碳酸钙含量的复合物复合前后PLA发生粘度变化，研究CaCO3对PLA/CaCO3复合物中PLA降解的抑制作用，并提出抑制机理。PLA/CaCO3复合物的力学性能和耐水性能的结果表明，添加一定量CaCO3的复合材料的拉伸强度、断裂伸长率、弹性模量和最大负荷明显增强。通过吸水率的测定，表明吸水率值随着CaCO3含量(2%和5%)的不同变化不大，而当含量增加到7%时，吸水率增大较多。随着吸水实验介质的不同，在磷酸盐缓冲溶液中浸泡的吸水率略高于在蒸馏水中浸泡的吸水率。 The poly (lactic acid) (PLA)/CaCO3 composites were prepared via melt blending in an intensive mixer of the torque rheometer. Hydrolytic degradation of the composites obtained was investigated comparatively with the pure PLA matrix. The hydrolytic degradation was carried out by immersing the film samples in phosphate buffer saline (pH = 7.4) at 37˚C, and the viscosity of the PLA in the degraded films was measured. The results indicated that the hydrolytic degradation of the PLA matrix in the composites was retarded as a result of the incorporation of the basic CaCO3 which would react with the partial end-carboxyl groups of the PLA matrix. It was showed that the tensile strength, elastic modulus, elongation at break and maximum load of the composites were enhanced significantly. Also it was found that the water absorption of the PLA/CaCO3 composites at low CaCO3 loading (2% and 5%) slightly increased compared with the pure PLA upon immersion for 4 weeks, while the PLA/CaCO3-7 composite had a much higher water absorption (5.5% - 6.0%) than the pure PLA in two immersion mediums. All composites exhibited slightly higher water resistance in the distilled water than in the phosphate buffer solution at pH = 7.4.

Viscoelastic, thermal, and morphological analysis of HDPE/EVA/CaCO3 ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO3), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (Tm) and the crystallization temperature (TC) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO3 was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO3, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO3 blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO3 with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO3 by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO3/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.

Toughness of HDPE/CaCO3 microcomposites prepared from masterbatch by melt blend method

AbstractIn this study, a series of high‐density polyethylene and micro/nanocalcium carbonate polymer composites (HDPE/CaCO3 nanocomposites) were prepared via melt blend technique using a twin screw extruder. Nanocomposite samples were prepared via injection molding for further testing. The effect of % loading of CaCO3 on mechanical and fracture toughness of these composites has been investigated in details. The effect of precrack length variation on the fracture toughness of the composite samples was evaluated, and the morphology of the fractured samples was also observed using scanning electron microscopy (SEM). It was found that increasing the % of CaCO3 and precrack length decreased the fracture toughness. Fracture surface examination by SEM indicated that the diminished fracture properties in the composites were caused by the aglomerization of CaCO3 particles which acted as stress concentrators. A finite element analysis using ANSYS was also carried out to understand the effect of agglomeration size, interaction between the particles and crack tip length on the fracture properties of these composites. Finally, a schematic presentation of the envisioned fracture processes was proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermomechanical properties of virgin and recycled polypropylene impact copolymer/CaCO3 nanocomposites

AbstractThe effect of successive injection moldings on the thermal, rheological, and mechanical properties of a polypropylene impact copolymer (PP) was investigated. The crystal content decreased as the molecular weight decreased due to chain scission with repeated injection molding. The Young modulus and the yield stress remained constant, despite a drop in the strain to break. Virgin and recycled PP matrix were filled with nanosized calcium carbonate (CaCO3) particles. The effect of morphology on the thermal and mechanical properties of nanocomposites of virgin and recycled PP filled with nanosized CaCO3 particles was also studied. The mechanical properties of the nanocomposites were strongly influenced by the intrinsic toughness of the matrix and the concentration and dispersion of the filler. The yield strength and strain of virgin PP decreased gradually, while its Young's modulus increased slightly with increasing CaCO3 loading. These phenomena were less pronounced for the recycled matrix. Incorporation of nanoparticles to virgin matrix produced an increase in tensile stiffness and ductility, when good dispersion of the filler was achieved. However, the impact strength dropped dramatically for high filler contents. A significant increase in impact strength was observed for the recycled PP. POLYM. ENG. SCI., 50:1904–1913, 2010. © 2010 Society of Plastics Engineers

Preparation and characterization of poly(ε-caprolactone)/calcium carbonate nanocomposites and nanocomposite foams

Biodegradable poly(ε-caprolactone) (PCL)/calcium carbonate (CaCO3) nanocomposites were prepared and characterized. Effect of CaCO3 on thermal and mechanical properties of PCL matrix was studied. Results showed that CaCO3 acts as a crystallization nucleating agent and introduction of CaCO3 leads to improved mechanical properties of the PCL matrix. PCL/CaCO3 nanocomposite foams were prepared using chemical foaming method. Cellular parameters such as mean cell size, cell wall thickness, and cell density were collected. The cellular structure of nanocomposite foams changes with different CaCO3 loading. Mean cell size achieved the minimum value at 5 wt% CaCO3 loading, and cell wall thickness increased with CaCO3 content. The changes in cellular structure and improvement of mechanical properties also enhanced the mechanical properties of PCL/CaCO3 nanocomposite foams. Compressive moduli of PCL/CaCO3 nanocomposite foams with similar density increased with increasing CaCO3 loading. POLYM. COMPOS., 31:1653–1661, 2010. © 2009 Society of Plastics Engineers

Blending Techniques Affecting Mechanical and Morphological Properties of Fly Ash/Ldpe and Caco3/LDPE Composites

The effects of blending methods on mechanical and morphological properties of CaCO3/LDPE and fly ash/LDPE composites were investigated as a function of filler loadings. The CaCO3/LDPE and fly ash/LDPE composites considered in this work were prepared by dry blending (high-speed mixer) and melt blending (using single- and twin-screw extruders). It was found that as the CaCO3 or FA loading was increased, the modulus and hardness for all blending techniques were increased, due to rigidities of the fillers and increased crystallinity level of the composites. Increasing the CaCO3 and FA loadings decreased the ultimate mechanical properties (tensile strength, elongation at break and impact strength) due to poor dispersion and interfacial defects of the composites. Composites prepared by the twin-screw extruder had the best mechanical properties as compared to those prepared by the dry blending or single-screw extruder, except for the impact strength. The overall mechanical properties of LDPE composites with CaCO3 were similar to those with FA particles, but the changes in the composite properties with CaCO3 particles were more sensitive than those with FA particles, this being associated with the differences in particle characteristics and dispersion level of CaCO3 or FA fillers.

Mechanical behavior of highly filled natural CaCO3 composites: Effect of particle size distribution and interface interactions

AbstractThe mechanical behavior of poly(di‐methyl siloxane) (PDMS) composites containing high volume fractions of natural CaCO3 particles of various particle size distributions was studied under tensile and oscillatory bending stresses, emphasizing the unique behavior of high filler loaded compositions. Composites containing the maximal possible solid loading of raw CaCO3 were investigated for the effect of fatty acids surface treatment. The elastic modulus increased with increasing filler loading, following Chantler's model for dental composites when correlated with the absolute filler volume fraction. Good fit to “traditional” models, e.g., Frankle‐Acrivos and Halpin‐Tsai, was obtained by correlating the modulus values with the volume fraction relative to the maximal possible filler loading. A master curve of different particle size distributions and filler levels composites was obtained by using the relative volume fraction values, illustrating the effect of particle packing characteristics on small deformation mechanical behavior. A minor increase in Tg was found in parallel to the appearance of a Tm relaxation peak at approximately −40°C. A peak temperature shift at Tm and a pronounced increase in this peak with increasing filler fraction was found as well. The changes in the melting transition are attributed to the constraints of the filler particles acting on the crosslinked melting polymer. Surface treatment with fatty acids significantly degraded the tensile properties. Interestingly, an increase of 4 vol% filler was enabled owing to the surface treatment, while restoring reasonable tensile properties. No significant effect was observed for excess of fatty acids resulting from physically adsorbed acids. Tan δ curves reveal low PDMS‐CaCO3 particles interactions, and mobility of the PDMS chains in the increased filler fraction as in the treated 64 vol% composite, both higher than those in the raw composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Rheology of highly filled natural CaCO3 composites: IV. Effect of surface treatment

AbstractThe rheology of poly(dimethyl siloxane) (PDMS) suspensions containing natural CaCO3 particles, treated with a homologous series of fatty acids, was studied using capillary and dynamic rheometry. Suspensions containing the maximal possible solid loading of raw CaCO3 were investigated, emphasizing the unique behavior of high filler loaded compositions. Surface treatment with fatty acids caused profound decrease of viscosity in the capillary flow, enabling a 4 vol% increase in the possible maximal solid loading of the suspension. The surface treatment leads to significant shear thinning opposed to the shear thickening exhibited by the untreated suspensions. Yet this effect was observed only at shear rates higher than 10 sec−1, while at lower shear rates and also under oscillatory low shear stresses, the opposite occurs: the viscosity of the surface treated systems increased. The contradictory effect of surface treatment at different shear rates regimes was ascribed to yield phenomenon of the treated suspensions, which is absent in the untreated ones. The combined, chemically and physically adsorbed acids caused higher increase in viscosity under oscillatory stresses, than the chemically adsorbed acids; thus, it can be concluded that thicker interface layer increased the yield effect reflected in higher viscosity at low shear rates. The oscillatory flow of the treated fine suspensions revealed also a consistent effect of the fatty acid length, the viscosity increased with increasing chain length; it correlated with higher layer thickness and higher surface energy of the treated filler, probably due to a skin friction effect. Copyright © 2007 John Wiley & Sons, Ltd.

Effect of Nano CaCO3 on thermal properties of Styrene Butadiene Rubber (SBR)

Styrene butadiene rubber (SBR) as matrix was reinforced separately with 9, 15 and 21 nm sizes of CaCO3, which were synthesized by matrix mediated growth technique. The mixing and compounding was done on two-roll mill and sheets were prepared in compression molding machine. The effect of nature and loading of nano CaCO3 on these rubber nanocomposites was investigated thoroughly by different characterizations such as DSC, TGA, XRD, and mechanical properties. An appreciable increase in glass transition temperature has been observed from DSC study. 9 nm sizes of CaCO3/SBR composites show more increment in Tg as compared to pristine SBR as well as different sizes of CaCO3 filled SBR. This increment in Tg is due to restricted mobility of nano CaCO3 filled SBR nanocomposites. XRD study of nanocomposites showed that nano CaCO3 dispersed uniformly throughout the matrix because of the small peak at lower 2θ. This uniform dispersion of nano CaCO3 contributes towards the higher mechanical properties of rubber composites. From TGA study, it was observed that as the size of CaCO3 reduces the thermal stability increases as compared to pristine SBR. The other results of these rubber nanocomposites were compared with commercial CaCO3 filled SBR.

Mechanical, Morphological and Thermal Properties of Rigid Polyurethane Foam: Effect of the Fillers

Rigid polyurethane foam (PUF) having different fillers such as precipitated silica (SiO2), precipitated calcium carbonate (CaCO3) and glass powder (GP) were prepared by blowing with distilled water. The effect of filler loading on different properties of PUF was studied. In this investigation, the filler content was varied from 5 to 50 parts per hundred of polyol (phr) by weight. The properties such as density, mechanical, morphological, water absorption, thermal conductivity and thermal properties of the filled PUF were compared with the neat PUF. The density of silica filled PUF decreases with an increase in the filler loading. In case of calcium carbonate and glass powder the density initially decreases with filler loading, but after a certain concentration of fillers there is an increase in density with filler content. The mechanical properties such as compressive stress at 10% strain, compressive modulus and hardness of the filled PUF decrease in comparison with the neat PUF, due to the reaction between isocyanate and surface functional group present in filler. In all cases, the water absorption of the PUF increases with the increase in filler loading, due to the decrease in the closed cell content. The thermal conductivity analysis of PUF shows that the insulation properties decrease with the increase in silica as well as CaCO3 loading. This is mainly due to formation of open and damaged cell structure. However, when glass powder is used as filler the thermal conductivity first decreases, but later increases with filler loading.

Comparative Study on Improvement in Mechanical and Flame Retarding Properties of Epoxy-CaCO3 Nano and Commercial Composites

ABSTRACT Commercial and nano calcium carbonate (CaCO3) filled epoxy composites were processed at 2 to 10 wt% compositions. Nano size CaCO3 was synthesized using in-situ deposition technique. Its nanosize and mixing with epoxy were confirmed by X-ray diffraction (XRD) method. X-ray diffractograms show that complete exfoliation occurs in the case of nanosize particles while micron size particles do not exfoliate. The effect of nanosize and commercial CaCO3 was studied on mechanical and flame retarding properties. The impact strength of composite increased up to 6 wt% loading of nano filler and further decreased. Young's modulus was observed at 1400 Mpa and 1100 Mpa for nano and commercial CaCO3, respectively at their 10 wt% loading, while pure epoxy showed 1000 Mpa; likewise, flame retarding properties improved six to four times on loading of nano and commercial CaCO3, respectively in comparison to pure epoxy resin. The improvement is due to exfoliation of nano in epoxy matrix, which is observed by X-ray diffractograms.

Mechanical and erosion properties of CaCO3‐EMAA thermal sprayed coatings

AbstractPolymer‐ceramic composite coatings manufactured from calcium carbonate and ethylene‐methacrylic acid copolymer (EMAA) were prepared via a thermal spray process employing different CaCO3 filler sizes (average size of 2.8, 9 or 36 μm) and loading levels from about 2.5 to 7 wt%. The optimum filler feeding characteristics, deposition efficiency and deposition rate were obtained with a 36 μm sized CaCO3. Tensile properties, peel strength, and the erosion resistance of a pure EMAA and CaCO3‐EMAA composite coatings were investigated. It was found that the tensile strain at fracture of the composite coating decreased with the addition of filler to a greater degree than that observed in compression‐molded polymer composites. This is attributed to an inhomogenous distribution of the filler, with more being concentrated at the boundaries of the deposited polymer particles, thereby establishing a rigid framework within the coating. Only a small filler content is necessary to establish large changes in the mechanical properties of the coating. The peel strength of a composite coating decreases with filler content, both on a mild steel substrate and a previously sprayed polymer coating. Bonding to the latter is significantly higher and offers a possibility as a bonding layer between substrates and composite coatings. The coefficient of friction is lowered with the addition of a filler. Erosion testing has shown that the erosion resistance of PF111 is little improved overall with filler addition, although some increase is found for filler contents less than 5 vol%. Polym. Eng. Sci. 44:1448–1459, 2004. © 2004 Society of Plastics Engineers.

Au Recovery Using an Activated Carbon Column

The feasibility of a process involving the use of activated carbon in a multistage column (NIMCIX contactor) for the recovery of gold from unclarified pregnant solutions was investigated on pilot-plant scale. It was found that satisfactory extractions, corresponding to a recovery of 99.6 percent, can be achieved with an average gold concentration of 0.0077 p.p.m. in the barren solutions from a feed averaging 1.89 p.p.m. The results show that excessive loading of CaCO3 can be prevented by lowering of the pH of the feed to about 7.6. This obviates the need for the carbon to be treated with hydrochloric acid. The gold was eluted from the carbon by the Zadra procedure. The operating conditions of the elution and electrowinning circuits are reported, and the elution of the gold and other metals is discussed. The reactivation of the carbon, which was carried out in a vibrating-deck kiln, is described, and the effects of this reactivation on the activity of the carbon and its microstructure are also discussed. The consumption of reagents in the adsorption and elution circuits is presented in sufficient detail to allow the potential of the activated-carbon process as an alternative to the Merrill-Crowe process for the treatment of high-grade solutions to be evaluated. In addition, the results of parallel small-scale investigations on the effect of pH on the loading of CaCO3, gold, and other metals on activated carbon are presented and discussed briefly.

The effects of oral CaCO3 loading and dietary calcium deprivation on plasma 1,25-dihydroxyvitamin D concentrations in healthy adults.

ABSTRACT Plasma 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations were observed to be inversely correlated with the urinary Ca/creatinine (r = –0.56) in 43 healthy adults eating ad libitum, suggesting that dietary Ca is one of the factors regulating the plasma concentration of this hormone. Increased Ca intake in 32 volunteers achieved by oral CaCO3 (39–130 mmol/day) for 4 days resulted in a rise in serum Ca within 6 h, hypercalciuria, a prompt fall in serum parathyroid hormone (PTH) and urinary cAMP/creatinine, followed by a sustained fall in plasma 1,25(OH)2D within 18–24 h from control levels of 84 ± 19 to 46 ± 28 pmol/liter (P < 0.001). A reduction in dietary Ca intake in six volunteers to only 1–3 mmol/day for 4 days resulted in a prompt fall in serum and urinary Ca, a rise in serum PTH an urinary cAMP/creatinine, and a sustained rise within 48 h of plasma 1,25(OH)2D concentrations from 63 ± 32 to 92 ± 28 pmol/liter (P < 0.05). For both groups, the changes in plasma 1,25(OH)2D were inversely correl...