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A digital balance Sartorius with 0. A sieve was used to determine the particle size of kaolinite clay powder.
Atomic absorption spectrometry AAS was used for elemental composition analysis. A differential scanning calorie meter DSC - and ATAT Thermo gravimeter analyzer was used for thermal analysis of synthesized zeolite and kaolin. The raw kaolin clay was wet beneficiated in order to purify it from physically and chemically combined impurities such as metallic oxide, soluble salts and impurities quartz, pebbles, plant remains and grits from the clay.
Different concentrations of sodium hydroxide was dissolved in distilled water in the reaction vessel, and then metakaolin was added to the sodium hydroxide solution gradually. After the crystallization, the resulting zeolite crystal was filtered and washed with demonized water until the pH was less than The FTIR spectra were used for qualitative characterization of surface functional groups of the kaolin. Functional groups present in the activated and raw kaolinite clay were confirmed before and after adsorption.
The total surface area of synthesized powder zeolite Na-X was measured using the standard volumetric method by nitrogen adsorption and application of the BET equation by means of a Nova BET instrument. The resulting BET equation is expressed as:. P and Po are the equilibrium and the saturation pressure of adsorbate at the temperature of adsorption, Q is the adsorbed gas quantity at STP, and Qm is the monolayer adsorbed gas quantity at STP.
C is the BET constant. Kaolin needs to be thermally activated in order to become reactive within the reaction mixture. This is promptly achieved by means of calcination, which provides enough energy to promote the required changes in the thermodynamic conditions. This process of activation results in drastic changes in the kaolin structure, drying it to lose its crystallinity.
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In the kaolin structure the Al atoms are octahedral coordinated with two vertex oxygen from the SiO 4 tetrahedral layer to an OH group from one side and three OH groups from the parallel hydroxyl layer from the other side. In the metakaolin, on the other hand, the Al atoms lose their initial configuration and are tetrahedrically coordinated.
This scenario is closer to the zeolite structure than that observed in the kaolin structure; thus metakaolin is suitable as raw material for zeolite synthesis. The band for absorption value at cm 1 was assigned for Si-O-Al, in which the Al is found in octahedral coordination. This indicated the synthesized zeolite is free from any contaminats or trace elements. However, in natural kaolin, some other minerals and oxides may be present before treatment and the absorbance value of natural kaolin is lower than the synthesized zeolite. Synthesized zeolite is therefore preferred over natural kaolin for adsorption.
A XRD diffractogram revealed structural defects in kaolin because of variability in the peak positions and modulation of their intensities in kaolin XRD patterns. This indicates that most of the zeolite amorphous material was being crystallized. A considerable amount of empirical data supports the idea that complexation can also result in substantial increases in metal adsorption above that observed in the absence of metal binding ligands.
The surface complexes have an effect for the adsorption of metal ions which corresponds to the surface area of the adsorbent. The common chemical composition analysis detected is the basic components of the kaolin mineral: aluminum oxide, silicon oxide and loss on ignition LoI.
As can be seen from oxide composition analysis of the synthesis zeolite, the silicon oxide percent by weight is much higher than the others and the inpurity responsible metal oxides Fe 2 O 3 , TiO 2 …. This shows that the synthesized zeolite is pure and has a potencial capacity for hardness adsorpition.
Differential scanning calorimetry DSC has been used to study the thermal effects during adsorption of Na-X samples. The dependence of the water uptake on temperature has been studied with a powdered sample. From this it can be deduced that synthesized zeolite from Ethiopian kaolin by the hydrothermal method can be used for water hardness removal.
The major functional group present in the natural kaolin was revealed by the FTIR spectra. Raw kaolinite before and after adsorption and synthesized zeolite's before and after ion exchange capacity were analyzed. Both samples showed same major peaks but their transmittance percentage intensity showed a wide range of differences. Comparing the samples, the synthesized zeolite showed the smallest peaks due to the replacement of the calcium and magnesium ions on the active surface of the adsorbent. FTIR spectra of synthesized zeolite: a raw kaolin; and b synthesized kaolin before and after adsorption of calcium and magnesium ions.
Contact time is inevitably a fundamental parameter in all transfer phenomena such as cation exchange process. The data showed that a contact time of minutes was required to achieve the equilibrium.
During the first few minutes of Na—X. It is found that the removal of hardness-producing ions increase with increase in contact time to some extent. Effects of contact time on calcium and magnesium removal with zeolite a and b effect of pH value on hardness removal. The pH of the solution is considered as an important factor affecting metal adsorption processes due to its impact on the degree of ionization of metal species and the surface charge of the adsorbent.
When pH was increased by NaOH addition, the precipitation phase was observed in the experiment. With further pH increase these precipitates gradually changed color at pH 7. This is due to the high degree of deprotonation of the functional group on the surface of hydrogen bond, which occurs at high pH. On the other hand, in neutral and alkaline media from pH 8—10 , the formation of metal hydroxide can be considered as the main reason for decreasing metal uptake. Temperature is another important factor that greatly influences the ion exchange process. The effect of solution temperature was investigated at K, K, and K.
Isotherms give an equilibrium relationship between the amounts of adsorbate adsorbed on the adsorbent surface and its concentration in the solution at a constant temperature.
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The two most important isotherm models are Langmuir and Freundlich. The Freundlich model is based on the assumption that metal ions are adsorbed on a heterogeneous surface and is not restricted to formation of monomolecular layer. From the Freunlich equation the value of Kf showed that the synthetic zeolite has a high adsorption capacity for calcium and magnesium ions.
Since the R 2 are fairly close to 1, thus both the models describe the system well.
However, the Langmuir isotherm model is more preferred than Freunlich isotherm. The results of the present investigation show that natural kaolin is an abundant and low cost material that can be synthesized for the removal of metals such as calcium and magnesium from water. Synthetic zeolite contains a high percentage SiO 2 , which makes it a useful material for hardness removal.
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The removal efficiency is influenced by the pH of the adsorbent. Equilibrium time after stirring is reached in minutes for synthetic zeolite. Low temperatures favor the removal of hardness. The removal rate of calcium increased from Experimental results were also evaluated with Langmuir and freundich isotherm models. The corresponding higher value of correlation coefficient monolayer capacity Qm and adsorption intensity n is determined from Langmuir isotherm and Freundilich isotherm respectively.
The result indicated that it was appropriate for calcium and magnesium metal adsorption. Generally, it can be concluded from this research that the adsorption capacity for calcium and magnesium ion removal is more significant for synthesized zeolite than raw kaolin for water hardness treatment. My sincere gratefulness goes to the staff of the Faculty of Chemical and Food Engineering, Bahir Dar Institute of Technology for their help and the institute for their financial funding, as well as providing access to all necessary materials for the successful completion of the research.
This article does not contain any studies with human participants or animals performed by any of the authors. Sign In or Create an Account. Advanced Search. Sign In. Article Navigation. Close mobile search navigation Article navigation. Volume 14, Issue 1. Previous Article Next Article.
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Research Article December 08 Removal of water hardness using zeolite synthesized from Ethiopian kaolin by hydrothermal method Tadele Assefa Aragaw Tadele Assefa Aragaw. This Site. Google Scholar. Water Practice and Technology 14 1 : Views Icon Views. Guest Access. In the principle of cation exchange, oxygen is bonded together to form a huge macro anion similar in structure to a macro molecule such as zeolite, NaAlSiO 4 Lijalem The essence is to dehydroxylat the beneficiated kaolin to form an activated amorphous material called metakaolin.
Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Hardness
The metakaolin was completely split into its silica and alumina components by complete delamination of metakaolin in excess acid. The dealumination process was carried out using 98 wt. Before and after hardness removal, zeolite samples were mixed with paraffin oil. The samples were then ground, desorbed and pressed to obtain IR transparent pellets.
The FT-IR was first calibrated for background signal scanning with a control sample of pure KBr and then the experimental samples were scanned. Differential scanning calorimetry DSC monitors heat effects associated with phase transitions and chemical reactions as a function of temperature and is a very informative method in physical characterization of a compound.
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Differential scanning calorimetry has been used to study the thermal effects of a zeolite Na-X sample. A STAT thermogravimetric analyzer was used for the thermal studies from the Bahir Dar Institute of Technology chemical analysis and characterization research grade laboratory. Lithium metborate fusion, HF attack, gravimetric and AAS analytical methods, from the geological survey of Ethiopia, were used for quantitative analysis of basic oxide compositions. Elemental concentrations in milligram per liter in the solution have been converted in to weight percentage oxide composition as shown in the equation below.
The adsorption measurements were investigated in batch experiments. The effect of adsorption temperature was also investigated at a temperature of , and K. The adsorption isotherms were studied by taking different initial concentrations of Ca and Mg ions in solution.
Until this study, investigation of the hardness of drinking water from different sources, and serum magnesium and calcium in normal subjects from the Surat district, had not been undertaken. This study was performed to assess the concentrations of calcium and magnesium, and total hardness in filtered and non-filtered water and the relationship with serum magnesium and calcium levels in normal subjects consuming such water.