Papers by Keyword: Precipitation

Abstract: Nickel is used as a raw material for Nickel Manganese Cobalt (NMC) batteries as a compound of Nickel Sulphate Hexahydrate (NiSO₄.6H₂O). This study used nickel laterite as ore. A hydrometallurgical process carries out Ferronickel to extract nickel concentrate. The first step is leaching using 2M H₂SO₄ solution for 6 hours with a stirring speed of 200 rpm at 90°C. The leached solution was then neutralized using a neutralizing agent MgO 5% w/w until it reached a pH of 3.5. The neutralized filtrate was then filtered to separate the filtrate and the residue. The neutralization process produces magnesium sulfate salt (MgSO₄), which is an impurity. Next, the cooling temperature method is used to precipitate MgSO₄ crystals. In this study, the variation of the MgSO₄ cooling temperature used was -5, 0, and 5 °C. Subsequently, crystallization was carried out to produce NiSO4.6H2O. The highest nickel recovery (59.61%) can be achieved using a cooling temperature of -5 °C. Also, by using -5 °C of cooling temperature, the nickel content of crystal product is 2.75%. The crystallization product still contains other compounds, such as MgSO₄, FeSO₄, and CoSO₄.

Abstract: Back-annealing during the hot dip galvanising (HDG) process was applied to heavily cold-worked low C-microalloyed VN steels in an attempt to achieve a yield strength of 700 MPa and a minimum A₈₀ elongation of 10 percent. HDG simulations were performed to compare recovery and recrystallisation kinetics in VN steel with that experienced in plain low C and Nb-Ti grades. Based on these results, an industrial melt was subjected to conventional hot rolling, cold rolling and back-annealing cycles during HDG. Precipitation in both VN and Nb-Ti steels extended the recovery window by about 75 degrees Celsius when compared to that found in low CMn steel. A temperature-time parameter M was used to compare the rates of softening. The M_rs (recrystallisation start) in both VN and Nb-Ti steels was 20.1 compared to 18 in a low CMn grade. The above properties were achieved by subjecting low C-microalloyed VN steel to low finishing and low coiling temperatures followed by back-annealing heavily cold-worked strip to a maximum temperature to prevent full recrystallisation. The softening rate during annealing is higher in both microalloyed steels than the CMn grade, with recrystallisation being completed more rapidly in the VN steel. Laboratory results implied insensitivity of restoration behaviour to hot rolling parameters whilst industrial results suggest that they are effective.

Abstract: This research aimed to study the recycling process and the feasibility of recovering iron as hematite or red oxide powder (Fe₂O₃) from spent pickling acid (hydrochloric acid). The spent hydrochloric acid waste from the pickling bath in the sheet rolling steel industry contains approximately 233 g of iron dissolved in one liter of the spent acid. To recover iron, 2 M NaOH was added to the spent acid until reaching pH 7. The iron was precipitated as iron oxide and/or hydroxide. Next, the oxidation of ferrous oxide was carried out by adding H₂O₂ 35%v/v to control the shade color. The precipitates were subsequently separated from the acid solution by a filter press. The precipitates were dried at 110°C for 24 h and calcined at 700°C for 2 h to synthesize and modify the crystallinity of ferric oxide. Ferric oxide was subject to water washing, where contaminating sodium chloride could be dissolved and filtered out. After drying at 110°C for 24 h, high-purity hematite was achieved. Hematite recovered from the spent pickling acid via this process provided more than 97% purity at 94.4% recovery.

Abstract: The rare earth element is a critical element in many industrial sectors. Due to unbalanced supply and demand, it is necessary to look for an alternative source. Coal ash is a waste product of power plant combustion. Previous research revealed that coal ash contained levels of rare earth elements. This research uses coal fly ash from the Paiton power plant. The objectives of this study were to determine the effect of the Na₂SO₄ concentration, stirring rate, and temperature on the recovery of REE concentrate. The experiment was conducted in four steps: (1) alkaline leaching, the process was carried out for 2 hours at 90°C with fly ash solid to 8 M NaOH solution ratio of 1:4 to break the aluminosilicate bonds. (2) Acid leaching of residue for 4 hours at 90°C in 3 M HCl. (3) Precipitation of residue to remove the impurities such as Fe using 1 M NaOH at pH 5. (4) Precipitation of filtrate from process (3) using Na₂SO₄ to produce REE concentrate precipitates. The best condition to obtain the highest REE residue is conducting recovery at the concentration of 20% Na2SO4, stirring rate of 500 rpm, and temperature of 50°C, with a yield of 88.72%.

Abstract: The separation process of Dysprosium (Dy) from other Rare Earth Elements (REE) in monazite was carried out considering various applications of Dy in high purity. The Dy elements can be used as a dopant in Thermoluminescence Detector (TLD) crystals to monitor the personnel dose of radiation workers. The separation process of Dy is hard to do due to the similarity of the physical and chemical properties of all REE. This research was conducted to separate Dy by a precipitation process at a certain pH. The feed used is Rare Earth Hydroxide (REOH) concentrate from a monazite processing. The variation of the precipitation used was pH 4.5 to pH 8.5 with 0.5 intervals. The highest precipitation of Dy with an efficiency of 24.47% was obtained at pH 8. Other REEs precipitated at pH 8.5, while the Dy was found the most in the filtrate.

Abstract: Salt is commonly produced from seawater by conventional solar evaporation process in Indonesia. Some of the salt produced has not been able to meet the standard requirement especially for industrial uses and make Indonesia still importing salt. This study aims to develop a precipitation model of various salt components during seasalt production from seawater by varying the brine input and output concentration on the crystallization table using the concept of solubility. The evaporation and precipitation processes during the salt production were modeled using a series of separator and filter units and carried out by making use of the electrolyte wizard in Aspen Plus^®. In this simulation, 9 variation were carried out by varying the brine input at concentration 20 ºBe, 23 ºBe, and 25 ºBe and output at concentration 29 ºBe, 30 ºBe, and 31 ºBe on the crystallization table. It is shown that the purity of NaCl salt is significantly influenced by the the brine input concentration to and the brine output concentration from the crystallization table. The percentage of calcium impurity increases when the brine input concentration to the crystallization table is lower while the percentage of magnesium impurity increases when the brine output concentration from the crystallization table is higher. The percentage of sulfate impurity increases when both the brine input concentration to and the brine output concentration from the crystallization table is lower. In practice, it is advisable that the crystallization in the salt table is carried out from 25 to 29 ºBe to limit the amount of magnesium impurity that can cause salt to taste bitter. Conducting the crystallization in this concentration range would give the purity of NaCl salt of 94.049%, which is in accordance with SNI standard for consumption salt, and the yield of NaCl salt of 78.83%. Further study needs to be done to provide a workable solution on how to make the purity of NaCl salt higher such as by using suitable precipitating agents in the salt production to help the precipitation process of various salt impurities.

Abstract: CoO nanocrystal is well-known photocatalyst for overall water splitting. However it suffers from a very short lifetime of only 1 h. The poor stability is derived from carrier recombination-induced thermal oxidation. This research will provide information about synthesis of CoO/ZnO nanocrystalline that can potentially enhance photocatalysts. CoO has been synthesized first under hydrothermal method, followed by calcination process. Thereafter, CoO has been used to produce CoO/ZnO under precipitation method. The samples were characterized using XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), and UV-VIS (UV–Visible Spectroscopy) to analyze their composition, chemical functional group, optical absorption, and band gap. The XRD spectrum showed that CoO/ZnO had cubic spinel and hexagonal phase structure with crystallite size of 69.0, 46.4, 32.8, and 32,4 nm. The bands in obtained FTIR spectrum at 586.36, 671.23, and 410-429 cm⁻¹ were correlated with vibrations of the Co³⁺ in octahedral hole, the Co²⁺ in tetrahedral hole, and Zn-O, respectively. The band gap energy of CoO, CoO/ZnO with variation of 1:1 and 1:3 were 4.39, 4.14, and 3.65 eV, respectively. The photocatalytic activities of CoO/ZnO were confirmed by methylene blue dyes photodegradation of 663 nm under UV light irradiation in aqueous solution. The 22.4% methylene blue can be removed within 3 h. Overall, these findings reveal the potential of CoO/ZnO for practical application.

Abstract: The aim of this work was to investigate the influences of different concentrations of Ag₃PO₄ aqueous dispersion by measuring the bacteriostatic characteristic against bacteria E. coli. The Ag₃PO₄ particles were successfully synthesized by precipitation method. Then, the morphological, structural and chemical compositional analyses were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. All these analyses confirmed the formation of Ag₃PO₄ particles with the shape of nearly spherical with a size of 100 – 700 nm. Meanwhile, Kirby-Bauer disk diffusion susceptibility test was chosen to determine the sensitivity of E. coli to antibacterial compounds in Ag₃PO₄ particles. The results showed that the antibacterial ability was significantly improved by increasing the concentration of Ag₃PO₄ aqueous dispersion, and the best concentration was 600 mg /mL. This study suggested that Ag₃PO₄ particles can be exploited as an effective candidate for antibacterial agents.

Abstract: Maraging steels are martensitic steels hardened by intermetallic compounds that precipitate during aging heat treatments. During aging of these steels complex phenomena involving nucleation and growth of several phases as well as changes in the precipitates, morphology and stoichiometry take place. The present work aims to study the kinetics of precipitation in a maraging 350 steel through the KJMA and Austin-Rickett (AR) equations. Analysed data were obtained from Vickers microhardness measurements carried out in samples heat-treated between 440 and 560 °C. Variation in the n-constant has been observed for both equations, indicating changes in the precipitation behavior. However, the n-constant values obtained from AR equation follow the microstructural changes observed in previous works on maraging steels. Interpretation of the n-constants using the AR equation was linked to the precipitation on dislocations at 440 °C, the growth of finite long cylinders in comparison to their separation at 480 °C, and general particle growth from small dimensions at 520, and 560 °C.

Abstract: As it is well established, Stokes law has been used to calculate the time required to precipitate a particle in a fluid under specific conditions such as sphericity, laminar flow, differences on densities (particle and fluid) and fluid viscosity for a specific gravity force (g). However, when the separation under 1-g takes days or months and it is crucial to estimate that time in just minutes, the separation time at 1-g can be estimated making a relationship with any other g (n). However, in any centrifuge the n value is not reached instantaneously but in a specific time and during this time the g-value is never constant, but it is always growing (at the first stage). Then, after reaching the n-value, the centrifuge could stay at that value for a certain time and then, (the third stage) the n value will change again, this time decreasing. Therefore, the aim of this study is to establish a mathematical model that considers the acceleration and deceleration periods and expresses them as equivalents of the n period by using a numerical approach [1-3]. It is expected the g-equivalent concept increases the certainty of the separation time estimation.