The effect of time variation on the results of increasing titanomagnetite in iron sand at magnetization temperature (800°C) with Na2SO4 addition as additive

Indonesia has rich deposit of Iron Sand that can be found along of the Java southern part island. Iron sand contains some Ti-Rich minerals such as ilmenite, titanomagnetite dan rutile. This study aims to determine the effect of time variation on the results of Increasing titanomagnetite in iron sand and addition of 15% Na 2 SO 4 as a catalyst. Variation of this reasearch was respectively 10 minutes, 20 minutes and 30 minutes with reduction temperature at 800°C. It takes the stage of roasting to condition the ore to be more easily reduced and increase the metal content so that it can maximize the iron sand purity with addition of Na 2 CO 3 additive with mass ratio 1:0.4. Based on the XRD and Semi-Quant equation using Software HighScore Plus, optimal time for reducing iron sand with coal at 800°C is 30 minutes, which produce content of titanomagnetite as much as 36%.


Introduction
Indonesia which is an archipelago country definitely has many river estuaries. Iron sand is widely spread along the south coast of java and generally has a very high Titanium content [1]. There are some minerals found in iron sand consist of magnetite, hematite, titanomagnetite and ilmenite. Titanium widely use for application in aeronauctics and biomedical science [2]. However, some industry also use titanium in the form of rutile (TiO2) as "White Pigment" especially for plastic and paper industry [3].
In this research, the process of increasing Ti content by reduction of iron sand which aims to form magnetite followed by magnetic separation with assumption that Ti bonded with Fe, which will form Pseudobrookite (Fe2TiO5), Ilmenite (FeTiO3), and Ulvospinel (Fe2TiO4).

Materials
The Iron sand samples used in this experiment were characterized using X-Ray Diffraction Spectrometry to observe the compund contained in a mineral semiquantitatively as seen as Figure 1. After that, Proximate and Ultimate Test have been done to determine the composition of Carbon in order to calculate total carbon required in this experiment.

Experiment
This reduction-roasting process is done using a muffle furnace. Samples of iron sand are processed by crushing and grinding up to 200 mesh. Then continued roasting at 800 O C for 2 hours with Na2CO3 addition with 1:0.4 ratio followed by quench. The water content of iron sand sample is removed by heating into oven at 120 O C for 20 hours. Before the reduction process, experiment is done by adding 5% Coal and Na2SO4 15% as fixed variable then continued by reduction with variation 10,20 and 30 Minutes at 800 O C.

Roasting process
The Roasting Process convert the entire magnetite phase into a hematite phase caused by the oxidation process of iron [7]- [9]. Based on XRD result, hematite phase is dominant phase formed on iron sand followed by the formation of Ilmenite with percetage of mineral as Table 4.  Addition of additive Na2CO3, not only aims to form alkaline complex phase when carried out, but also aids the separation of Fe2O3 with alumina by following reaction : Al2O3(s) + Na2CO3(s)  Na2Al2O4(s) + CO2(g) Then proceed with leach using aquadest so that it will increase the pH of the water to 12-14 by the following reaction :

Fig. 3. Pourbaix diagram of Al2O3
After water quech process, the water itself was tested by pH meter. it shows that the acidity level is 12. In the pourbaix diagram which can be seen in Figure 3, Al2O3 shows that it can change to its ionic form AlO2so that the predicted alumina on the sample will dissolve during water quench process. We can conclude that the Al impurities is eliminated and it is in accordance with the literature.

3.2.
Reduction process From the XRD result and semi-quantitative data obtained from High Score Plus Software on the reduction process there is an increase of magnetite and titanomagnetite compunds due to reduction process which influenced by %FeO. It can be seen from ternary diagram FeO-TiO2-Fe2O3 in Fig. that increasing %FeO will initiate the form of Magnetite and Ulvospinel. The initiation of Magnetite and Ulvospinel leads the form of Titanomagnetite which Titanomagnetite is formed by solid solution mechanism between Magnetite and Ulvospinel. Its formation can be seen based on reaction below : The reduction process leads to a partial transformation of the hematite-ilmenite phase into a magnetitetitanomagnetite phase since both are co-existent minerals. On the other hand, an increased level of magnetite from initial iron sand at variable 20 Minutes and 30 Minutes with magnetite concentration are 24.2%, 25.9% and 51.1% respectively. While, titanomagmetite concentration are 16.4%, 22.7% and 36% respectively. Anomaly was shown in variable 10 minute with magnetite and titanomagnetite level are 51.6% and 28.4%, it is caused by the difference of working procedure so that the pyrolysis last longer than 20 Minute variable.
The addition of Na2SO4 will accelerate the reduction process, due to the mechanism of sodium sulphate cristallyzation damage which will lead to the formation of micropores in iron sand [11], [12].

Conclusion
The optimum point of Titanomagnetite formation is shown at the time of iron sand reduction for 30 minutes with semi-quant level by 36%, so it could be understood the longer time reduction process of solid solution formation between ulvospinel and magnetite will be maximal. Addition of Na2CO3 to the alkaline roasting process followed by wuenching process using aquadest aims to remove impurities in the form of alumunium. Then the addition of Na2SO4 to reduction serves as a catalyst in the reduction process