Rare Earth Element plus Yttrium (REY) is an essential element in the modern industry. Due to its limited supply, REY recovery from alternative sources is needed. Coal fly ash is one of the candidates of REY sources. Coal fly ash taken from the pulverized coal power plant in West Java was used as a raw material in this research. A sequential process of alkaline digestion and acidic leaching was applied for enriching and recovering REY from this coal fly ash. The enriching step using alkaline digestion produced desilicated residue with higher REY concentration than the raw coal fly ash. The sulfuric acid solvent was used for leaching the desilicated residue in this work to investigate its effect on REY recovery. The highest REY recovery obtained in this work was 75.25% which recovery process condition using 1 M H2SO4 concentration, liquid to solid (L/S) ratio of 25 (mL/g) and 30 minutes leaching time.

Recovery of Rare Earth Elements (REE) from waste is an important alternative to solve global REE crisis. Therefore, coal fly ash containing REE becomes a potential candidate as an alternative source of REE. Indonesia has a large potential of coal resources, however unlike other type of coals which is rich in SiO 2 and Al 2 O 3 , Indonesian coal contains significant amount of Fe 2 O 3. As a consequence, fly ash resulted from burning Indonesia coal is also rich in iron oxides. The presence of high concentration of iron oxides will however reduce effectiveness of REE recovery from coal ash through hydrometallurgy process. Therefore, iron oxides in the coal fly ash needs, firstly, to separate preceding further REE separation. This study determined the optimal process conditions in the iron recovery process from coal fly ash. The variables studied were fly ash grain size, magnetic field strength and separation techniques. The iron recovery was determined by mean of the ratio of iron concentration after and before magnetic separation. Experimental results showed that increasing magnetic field strength and decreasing coal fly ash grain size in a wet separation will increase the recovery of magnetic iron component. Magnetic field strength of 4300 Gauss and grain size of-400 mesh were the optimal values in this study with iron recovery of 25.89%.

Surge is major problem in compression system especially in process industries. Typically, surge can be eliminated by providing the compressor anti-surge controller based on proportional integral derivative (PID) control or model predictive control (MPC). This study designed and evaluated the performance of MPC at centrifugal compressor in ammonia plant. The MPC is compared with the existing and tuned PID control. The evaluation results show that the performance of designed MPC is better than PID control for compressor anti-surge control in ammonia plant.

The presence of static friction or stiction in a valve can lead to poor performance in industrial automation and control system. This paper presents a method to detect and quantify stiction based on normality test and Hammerstein system identification. Detection and quantification are showed by the f s and f d parameters, where the value of f s and f d greater than 0 indicate the valve suffer from stiction. The proposed method is implemented to a confirmed sets of industrial data as a validation. The result show that the proposed method can accurately detect the presence of stiction and distinguish it to other problem in control loops.