Mirwan, A., & SusiantoHandogo, R., 2017. A Modified Shrinking Core Model for Leaching of Aluminum from Sludge Solid Waste of Drinking Water Treatment . International Journal of Technology. Volume 8(1), pp.19-26
|Agus Mirwan||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Surabaya 60111, Indonesia|
|Susianto||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Surabaya 60111, Indonesia|
|Renanto Handogo||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Surabaya 60111, Indonesia|
Aluminum; Leaching; Recovery; Shrinking core model; Sludge solid waste
SSW was collected from the sludge ponds of DWT Banjarmasin, Indonesia; washed and dried under direct sunlight for 24 hours; and then oven-dried at 105°C for 3 hours. It was milled in a grinder and then sieved to select particles that were 0.074-0.044 mm in width, with a particle size of 0.0585 mm, before the leaching process was carried out.
2.2. Leaching Procedure
About 5 g (measured exactly) of grinded and classified SSW was extracted with 250 ml of 4 M hydrochloric acid (HCl) (prepared from Sigma-Aldrich with a purity of ? 32%) in an Iwaki Pyrex boiling flask. The flask had one neck for a thermometer and for the inlet or withdrawal of samples at regular time intervals (3-60 minutes). The reaction mixture was stirred at 300 r.min-1 using a magnetic stirrer and was heated (Dragon Lab, MS-H-Pro, People's Republic of China) indirectly through a water bath at different temperatures (30, 50, 70, and 90ºC). At selected time intervals (5, 10, 20, 30, 40, 50, and 60 minutes), all samples were collected using a syringe and filtered for analysis to determine the aluminum content in the solution using an inductively coupled plasma cluster optical emission spectrometer (ICP-OES) (9060-D Teledyne Leeman Labs. the USA). Each analysis was repeated three times and deputized with average values.
The total amount of aluminum can be leached out in the acid condition and calculated based on standard methods (Cheng et al., 2012). SSW was added in nitric acid with a ratio of 1:1 and filtered. The filtrate was analyzed using ICP-OES to determine the amount of soluble aluminum. The result indicated that approximately 61.8 mg of aluminum ions can leach from 1 g of WTS, and the aluminum leaching recovery (x) can be stated as , where X0 denotes the total aluminum obtained through the acid leaching process, and X is the amount of aluminum obtained at different conditions (mg/g).
2.3. Model Development
According to Cheng et al. (2012), a lower pH between 1 and 3 in aluminum dissolution can be obtained with a higher aluminum recovery ratio of approximately 70-90%. Furthermore, at normal temperatures, Al2O3 cannot react with acid so that the solid-phase amorphous aluminum hydroxide contained in sludge can be leached out by the acidification process. Chemical reactions that occur in SSW and hydrochloric acid are stated as follows:
Al(OH)3 (s) + 3HCl (aq) ? AlCl3 (aq) + 3H2O
Figure 1 Schematic drawing of the SC model
2.4. Mathematical Modeling of Leaching Kinetics
SC model assumptions are as follows: SSW has spherical particles; the particles are completely mixed so that their spherical shape can be maintained; the temperature is fixed during the leaching process; other substances in the SSW do not have a significant effect on the kinetics (Safari et al., 2009).The total mass balance equation for leaching is as follows:
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