Shand Sulfuric acid; use and handling by Oscar T. Wording Edition Chemicals. What is MDS? LibraryThing's MDS system is based on the classification work of libraries around the world, whose assignments are not copyrightable. MDS "scheduldes" the words that describe the numbers are user-added, and based on public domain editions of the system. A study by Suwanthai et al. This improvement was due to the reaction of HCO 3 - in aqueous solution during the slaking reaction process.
Valuable information from their work shows that they were able to eliminate the influence of impurities during the carbonation reaction. Furthermore, Chen el al. In their study, they observed that particle morphology and nucleation were closely related to the reaction pH of solution. The recarbonation process is the most common technique of producing PCC. Carbonation is generally carried out in a series of reactors under closely controlled operating conditions to produce the required PCC morphology and particle size distribution PSD. Luo el al. They reported that buffer solution highly influence the polymorphic phase of PCC while CO 2 concentration and rate of gas flow have no significant influence.
Furthermore, high purity spherical vaterite particles can be synthesized under controlled reaction conditions. This work investigates the transition effects of reactant concentration and gas flow rate on PCC morphology and crystallite size using gas-liquid route via a modified batch-wise, bubble-column type reactor. Materials and Experimental Methodology. In this research, limestone used for the experiments was calcined in a muffle furnace at an optimum disassociation temperature and resident time. However, the impurity does not present any significant discoloration in the final PCC.
Chunks of limestone were crushed into a manageable size range of mm diameter before calcined in a muffle furnace at an optimum disassociation temperature and resident time. The resulted quicklime is then hydrolyzed into distilled water to produce creamy hydrated-lime.
In the slaking process, lumps of quicklime disintegrated to produce creamy white smooth paste of hydrated-lime Ca OH 2 suspension, and is subsequently diluted in excess distilled water to produce different 'milk of lime' molarities. Presence of trace amount of aluminium-silicate bearing minerals such as fine clay particles, carbonaceous matters, over burned or residual calcium carbonate generally has insignificant effect on the slaking process.
The resulted PCC produced from various experimental designs were carried out to characterize its crystal morphology, particle size distribution pattern, state of agglomeration, and chemical purity.
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Table 1 shows the experimental designs for these experiments. These experiments were carried out in a one liter modified batch-wise, bubble-column type reactor Fig. The experiment was designed to investigate and foresee the influence of reactant concentration and gas flow rate towards resulted PCC characteristics and precipitation process mechanisms. This is especially in the terms of crystal morphology and growth sizes of PCC formed under specific operating conditions and parameters setting. In this case, precipitation or recarbonation processes were conducted at two predetermined CO 2 gas flow rates over a period of 60 and 90 min resident time.
Reactant concentrations were fixed between 0. Effects of the concentration and CO 2 flow rates on particle morphology and size were investigated. Prior to SEM examination, these PCC powders were dispersed in methanol and ultrasoni-cally treated to reduce particle aggregation. Results and Discussion. The rate of recarbonation seems directly related to the reactant concentration, bubbling time and CO 2 gas flow rate conditions, and eventually affects the characteristics of the resulting PCC.
Ca OH 2 aq. Effects on Conductivity and pH. Reactant concentration at a particular time during the course of the reaction can be monitored by conductivity and pH.
During the course of precipitation, the pH, conductivity Fig. At low initial concentrations, the solid Ca OH 2 is rapidly dissolved and depleted in a short period of time during the course of precipitation to form PCC crystallite. This consequently will affect the characteristics of produced PCC, e. Progress in recarbonation, gradually generated CaCO 3 in the form of solids particles less dissolved species , hence reduces the electrokinetic ability as well as resulted to decrease in conductivity ability.
Higher reactant concentrations need a longer bubbling time, and this can be compensated by increasing the gas flow rate. Excess gas supply only resulted in dissolved CO 2 to form a weak HCO 3 - , and normally show a slight rebound in conductivity values Fig. Figure 3 shows a sudden and brief peak-up in resistivity values, which occurred at the same 'dropped points' as in pH and conductivity trends. TDS values were also exhibiting similar trend as in conductivity and pH. Higher reactant concentration of 2. This can also be shortened by increasing the gas flow rate.
However, morphology and other crystal characteristic of resulted PCC would not be the same. PCC precipitation is an exothermic chemical reaction. Higher reactant concentrations e. M in PCC F2 yielded greater amount of heat as compared to the lower one. Gradual increase in intensity was in tandem with phase concentration or growth rate of PCC followed by the reduction of Ca OH 2. Irrespective of reactant temperature, the growth rate of PCC increased with longer bubbling times. XRD pattern for experimental design as shown in Table 1 is almost identical and consistent because of the complete formation to calcite phase in all experimented samples.
All the samples show almost similar peak position and intensity. No peaks of Ca OH 2 was present, thus indicating a complete recarbonation. Marked different in crystal morphology characteristics as shown by SEM micrographs Fig. FTIR spectrum shows typical absorption peaks of calcite around , and cm -1 Fig.
This indicates that the formed PCC have, somewhat, variation in crystal morphology or atomic structure during precipitation, which is hard to be defined by the XRD spectrum.
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Chemical Composition and Purity. The mass loss corresponds to the released amount of CO 2 44 wt. Results indicated that the produced PCC is very high in purity with an average of about Other components, which are normally inherited from precursor stone are often less than 1. Crystal Morphology. Figure 4 shows examples of the crystal phases of PCC produced at the selected concentrations, gas flow rates and bubbling times.
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Generally, calcium carbonate mineral phases crystallized into three common crystal polymorphs calcite, aragonite and vaterite. However, there are other crystal morphologies that have been discovered depending on different kind of operating techniques and reactant used. At ambient conditions, calcite is a thermodynamically stable form of carbonate and has cubical rhombohedra crystal morphology.
At a lower reactant concentration e. Change Language. Arabic English. Important Links. Follow Us. App Download. US UK.
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