REDUCTION OF IRON CONCENTRATION IN SPENT ELECTROLYTE TIN ELECTROPLATING PROCESS WITH EUTECTIC FREEZE CRYSTALLIZATION AND CEMENTATION

• Main Author: ARIEF PURNOMO (NIM : 12513004), MUHAMMAD
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/29129
• Institution: Institut Teknologi Bandung

Based on the Annual Report of International Tin Research Institute in 2016, Indonesia ranks second as the largest tin producer in the world after China. Total tin production in Indonesia in 2016 is 696,000 tons[1]. In general, pure tin is used for the manufacturing of solder, tinplate, copper alloy, and battery. One of the methods to produce tinplate is electroplating. The dissolution of iron from steel workpieces into electrolytes is a major problem because it narrows the applicable operating density and accelerates the oxidation of Sn2+ to Sn4+ which decreases the current efficiency and product quality. There are several methods that can be applied for handling spent electrolyte. The method of dilution with fresh electrolyte requires a high cost. Other methods such as chemical precipitation can not separate tin from iron because tin is deposited at a lower pH than iron. In this research we studied the separation of Sn and Fe in spent electrolyte tin plating with Eutectic Freeze Crystallization (EFC) method and Sn cementation using iron powder. <br /> <br /> <br /> <br /> <br /> The sample used is spent electrolyte which is waste from tin electroplating plant, PT Pelat Timah Nusantara Tbk. Sample preparation was performed by homogenizing the solution in an agitated chemical glass in room temperature using a magnetic stirrer. It was intended that there was no precipitate in the spent electrolyte. Furthermore, concentrations of Fe and Sn were measured using AAS (Atomic Absorption Spectroscopy) and Fourier Transform Infrared Spectroscopy (FTIR) analysis to determine the functional groups of organic compounds in spent electrolyte. The EFC experiment was performed in a reactor that covered by sterofoam and connected with thermocouple. Dry ice is used to lower the temperature of the methanol bath at the EFC reactors to -7, 17, -23, and -30oC. Variations of EFC experiments were agitation speeds of 50, 100, 150, and 200 rpm and the ratio of volume of methanesulfonic acid (MSA) to sample volumes of 5/250, 10/250, 15/250, and 20/250. Meanwhile, in the cementation experiment, temperature variations were performed at 25, 50, 75, and 95oC and iron stoichiometric mole of dissolved Sn (0.5x, 1x, 1.5x, and 2x). The cementation experiment was conducted in a five-necked reactor connected to a condenser, hot plate and magnetic stirrer. <br /> <br /> <br /> <br /> <br /> EFC experiments indicate that the lower the temperature, the higher the percent crystallization of iron and tin. The highest reduction percentage of iron and tin was obtained at -30°C, such as 98.73% and 45.95% respectively. In the EFC experiment, the agitation speed of 200 rpm gave the largest iron percent reduction percentage of 98.03% and the percentage of reduced tin was 45.91%. The final iron concentration <5 g/L was obtained at agitating speeds of 150 and 200 rpm, temperature -17, -23, and -30oC. Variation of MSA volume ratio to sample volume of 20/250 solution gave the highest iron and tin reduction percentage that was 98.73% and 45.95% respectively. The EFC experiments with the MSA ratio of 15/250 and 20/250 and the temperature of -17, -23 and -30oC was succeeded in decreasing the concentration of Fe <5 g/L in the final electrolyte. The Sn cementation experiments with Fe powder do not provide sufficient tin precipitation percentage where the highest percent of Sn precipitation is 30.51% that obtained at 95°C with the addition of Fe 2x stoichiometric powder. <br />