Adhesion of in situ precipitated calcium carbonate in the presence and absence of magnetic field in quiescent conditions on different solid surfaces

Deposition of in situ precipitated calcium carbonate from Na(2)CO(3) and CaCl2 solutions on different substrates, i.e. stainless steel, copper, aluminium, and glass, was investigated at different temperatures, 20 degrees C, 40 degrees C, 60 degrees C and 80 degrees C, both in the absence and presence of S-S 0.1T magnetic field (MF). It was found that in quiescent conditions during 2h the amounts deposited firmly on the surfaces decreased with increasing temperature. If MF was present the deposition was reduced at all temperatures, and depended on the nature of the substrate. The largest MF effect was found on glass at 60 degrees C, which amounted 50% reduction of the deposit. However, at 80 degrees C no deposition was found in the presence of MF on aluminium surface. At this temperature the reproducibility of the experiments was poor, and an additional effect due to the metal surface corrosion (especially that of aluminium and copper) may be thought in alkaline environment of the experiments (pH ca. 10). Based on optical microscope photographs, it was concluded that the amounts of crystallographic forms of CaCO3 depended on the nature of substrate on which the precipitation and then the adhesion took place. To some extent the ratios of CaCO3 forms precipitated were different in the bulk phase than on the substrate surfaces at the same temperature, and this conclusion was based on the X-ray diffractograms. Some possible mechanisms causing MF effects are discussed.     

利用钢渣固结CO_2制备沉淀碳酸钙的试验研究

研究了基于醋酸提取钢渣中钙离子所获得的醋酸钙溶液碳化固结CO2并制备沉淀碳酸钙的可行性,借助于XRD,TG-DTA对碳化后生成的沉淀物进行了成分分析和综合热分析.结果表明:醋酸钙溶液需掺入氢氧化钠,将其中的醋酸钙转化成氢氧化钙,方可碳化生成沉淀碳酸钙;在由醋酸提取钢渣中钙离子所获得的醋酸钙溶液中掺入足量氢氧化钠,可使其中的钙离子碳化生成沉淀碳酸钙,但该碳酸钙的纯度(质量分数)仅为60%左右,钙离子转化率(质量分数)仅为35.00%左右,如果将该溶液进行分离处理,除去其中其他离子的干扰,则可高效碳化成高纯度沉淀碳酸钙.     

Effect of a magnetic water treatment on homogeneous and heterogeneous precipitation of calcium carbonate

In this paper are reported experimental results on the effect of a magnetic field on the precipitation process of calcium carbonate scale from a hard water. Carbonically pure water was circulated at a constant flow rate in a magnetic field. After this treatment, calcium carbonate precipitation was induced by degassing dissolved carbonic gas. The nucleation time was identified from the variations of the pH and the Ca(2+) concentration. The ratio between homogeneous and heterogeneous nucleation was determined from the measurement of the mass of precipitated calcium carbonate. It is shown that the magnetic treatment increases the total amount of precipitate. This effect depends on the solution pH, the flow rate and the duration of the treatment. In addition, the magnetic treatment modifies the ratio between homogeneous/heterogeneous nucleation. Homogeneous nucleation is promoted by an increasing the pH of water, the flow rate as well as the residence time. The magnetic treatment enhances these effects with a maximum for a 15 min treatment time. It is shown that the presence of calcium carbonate colloid particles is not necessary. It is advanced that the main magnetic effects concern the associations of ionic species which are present in the solution and which are involved in the nucleation process of calcium carbonate precipitation.     

Evaluation of the salt accumulation process during inundation in water resource of Contas river basin (Bahia-Brazil) applying principal component analysis

The high salinization in some reservoirs of the Contas river basin (Bahia-Brazil) has been erroneously attributed only to concentration by evaporation. However, recent studies of this basin have shown that in period of intense rainfalls, occur an increase of the saline concentration in the flowing rivers of the reservoirs. The application of statistical methods (cluster and principal components analysis) have shown that this fact can be attributed to the discharge of saline waters from the small reservoirs of every drained area, provoked by inundation, is also an important factor in the salinization process. Thus the study of the geochemical variables: Na(+), K(+), Ca(2+), Mg(2+), Cl(-), SO(4)(2-) and CO(3)(2-), showed one group formed by Na(+) and Cl(-), attributed to the discharge of saline water provoked by inundation from a small reservoir, and a second group constituted by Ca(2+), Mg(2+), K(+) and SO(4)(2-), due to an increase provoked by the evaporation in the salinization process.     

Effect of pH and temperature on calcium carbonate precipitation by CO2 removal from iron‐rich water

In the present work, the effect of temperature and solution pH on calcium carbonate precipitation from iron‐rich waters was investigated. Calcium carbonate was precipitated by CO₂ removal. The increase in the temperature or the solution pH leads to the acceleration of calcium carbonate nucleation and crystal growth. Iron addition retards the formation of calcium carbonate crystals and enhanced the precipitation in the bulk solution. At high supersaturations, the inhibition effectiveness of iron is small and it could be improved by lowering the solution pH. The results of the present work show that it is possible to reduce or completely prevent scale formation in different water treatment processes by controlling the operating parameters which favourably affects the water treatment costs, increases the equipment life and allows increased product water recovery.     

A spectrophotometer-based study of magnetic water treatment: assessment of ionic vs. surface mechanisms

A technique previously used to study the effects of magnetic fields on calcium carbonate (CaCO3) precipitate is revisited in order to investigate the two most widely reported mechanisms. The laboratory-based study tested the effect of treating solutions and particulates of CaCO3 and showed that a repeatable magnetic effect on precipitation is observed, but only when CaCO3 particulates are exposed to magnetic fields, and not when a solution of sodium carbonate (Na2CO3) is exposed to magnetic fields. Issues regarding the reproducibility of the test are also discussed.     

Assessment of groundwater quality and its suitability for agricultural usage in and around Rangampeta area,Andhra Pradesh,south India

The aim of this study is to assess the groundwater quality of Rangampeta area for irrigation and domestic purposes. The groundwater samples were analyzed for distribution of chemical elements Ca, Mg, Na, K, Si, HCO₃, CO₃, Cl and SO₄. It also includes pH, electrical conductivity, total hardness, non carbonate hardness and total alkalinity. The parameters like sodium absorption ratio, adjusted sodium absorption ratio, sodium percentage, potential salinity, permeability index and residual sodium carbonate were calculated. The dominant hydrochemical facies of groundwater are Ca–Mg–Cl and Na–Cl Water Types. The Gibbs’s diagram plots suggest that the chemical weathering of rock forming minerals is the major driving force controlling water chemistry in this area. The positive chloro-alkaline indices revealed that the groundwater has suffered ion exchange between Na and K of water with Ca and Mg of soil during its flow.     

碳酸钠污染重塑黏土微观结构的试验研究

,利用扫描电镜(SEM)观测浸泡试验制备的不同浓度的碳酸钠(Na2CO3)污染重塑黏土的微观结构,而后利用Matlab提取出污染重塑黏土的表观孔隙率和表观孔径分布,并进一步探讨Na2CO3对污染重塑黏土微观结构的改造机理。研究表明:经Na2CO3污染侵蚀后,重塑黏土的絮状结构遭到破坏,颗粒与孔隙重新分布,孔隙率显著降低;基于手动选取最佳阈值,利用Matlab提取的污染重塑黏土表观孔隙率随Na2CO3侵蚀程度的提高显著降低,表观孔径呈现出以大孔和中孔为主逐渐演化为以小孔和微孔为主的分布特征;Na2CO3通过与黏土颗粒的离子交换和吸附,与非碱金属阳离子和游离氧化物的化学反应以及与腐植酸的中和作用,实现对黏土微观结构的多元化改造。     

The simultaneous removal of calcium and chloride ions from calcium chloride solution using magnesium-aluminum oxide

We investigated the removal of Ca(2+) and Cl(-) from CaCl(2) solution at 20-60 degrees C, using magnesium-aluminum oxide, Mg(0.80)Al(0.20)O(1.10), prepared by the thermal decomposition of a hydrotalcite-like compound, Mg(0.80)Al(0.20)(OH)(2)(CO(3))(0.10).0.78 H(2)O. The degree of Ca(2+) and Cl(-) removal from the solution increased with increasing initial CaCl(2) concentration, temperature, and quantity of Mg(0.80)Al(0.20)O(1.10) added. When Mg(0.80)Al(0.20)O(1.10) was added to 0.25 M CaCl(2) solution in a Mg(0.80)Al(0.20)O(1.10)/CaCl(2) molar ratio of 20, the degree of Ca(2+) and Cl(-) removal from the solution at 60 degrees C after 0.5 h was 93.0% and 98.2%, respectively. These results reveal that Mg(0.80)Al(0.20)O(1.10) has the capacity to remove Ca(2+) and Cl(-) simultaneously from aqueous solution.     

Bioaccumulation of nickel from aqueous solutions by genetically engineered Escherichia coli

This study constructed a genetically engineered Escherichia coli JM109 which simultaneously expressed nickel transport system and metallothionein to remove and recover Ni(2+) from aqueous solution. Bioaccumulation process was rapid and followed linearized Langmuir isotherm. A more than six-fold increase of Ni(2+) binding capacity was obtained by genetically engineered E. coli cells compared with original host E. coli cells. A pH assay showed genetically engineered E. coli cells accumulated Ni(2+) effectively over a broad range of pH (4-10). The presence of 1000 mg/L Na(+) and Ca(2+), or 50mg/L Cd(2+) or Pb(2+) did not have a significant effect on Ni(2+) bioaccumulation, while Mg(2+), Hg(2+) and Cu(2+) posed a severe adverse influence on Ni(2+) uptake by genetically engineered E. coli. Furthermore, genetically engineered E. coli cells did not require extra nutrients for Ni(2+) bioaccumulation.