Pengendapan Torium (Th) dari Monasit Bangka Setelah Proses Solvent Impregnated Resin (SIR)

ABSTRAKPengolahan monasit Bangka secara basa dilakukan melalui tahapan dekomposisi; pelarutan parsial pH 3,7; pengendapan parsial pH 6,3; dan pengendapan total pH 9,8. Proses tersebut menghasilkan natrium fosfat, Rare Earth (RE) hidroksida, uranium (U), dan torium (Th). Pada proses dekomposisi, 99 % natrium fosfat telah terambil dan RE hidroksida telah terpisah dari U dan Th dengan recovery 85 %. Sementara itu, U dan Th yang dihasilkan masih bercampur sehingga perlu dipisahkan. Pemurnian Th dari U pada monasit telah dilakukan dengan metode Solvent Impregnated Resin (SIR) dan dilanjutkan dengan proses elusi setelah SIR. Hasilnya, Th masih berada pada fase cairan berupa larutan torium nitrat [Th(NO3)2] sehingga perlu diendapkan sebagai torium hidroksida [Th(OH)2] untuk memudahkan proses berikutnya. Pengendapan Th setelah proses SIR dilakukan dengan tujuan memperoleh kondisi optimum pengendapan. Resin penyokong yang digunakan adalah amberlite XAD-16 menggunakan ekstraktan yang diimpregnasikan dengan tributyl phosphate (TBP), reagen elusi asam nitrat (HNO3) encer dan reagen pengendapan amoniak (NH4OH). Parameter yang diteliti adalah pengaruh pH dan waktu pengendapan terhadap recovery Th. Hasil penelitian menunjukkan kondisi optimum pengendapan Th dari monasit setelah proses SIR pada pH 1,2 dan waktu 60 menit dengan recovery 84,74 % Th; 3,26 % U; 34,74 % RE; dan 8,52 % PO4.ABSTRACTAlkaline processing of Bangka monazite is carried out through stages like decomposition; partial dissolution pH 3.7; partial precipitation pH 6.3; and total precipitation pH 9.8. These procesess produce sodium phosphate, Rare Earth (RE) Hydroxide, uranium (U), and thorium (Th). On decomposition procsess, 99 % of sodium phosphate had been recovered and RE Hydroxide was separated from U and Th with 85% recovery. Meanwhile, the U and Th products were still mixed so that needs to separate. Purification of Th from U in monazite had been carried out by using Solvent Impregnated Resin (SIR) method and continued by elution after SIR. The result is that Th is still in the liquid phase as thorium nitrate [Th(NO3)2] solution so it needs to be precipitated as thorium hydroxide [Th(OH)2] to facilitate the next process. Precipitation of Th after SIR process is conducted with the aim to obtain optimum precipitation condition. The supporting resin used is amberlite XAD-16 with impregnated tributyl phosphate (TBP) extractant, dilute nitric acid (HNO3) as elution reagent, and ammonium hydroxide (NH4OH) as precipitation reagent. The observed parameters are the effect of pH and precipitation time on Th recovery. The results show that the optimum precipitation conditions of Th from monazite after SIR process is on pH 1.2 and 60 minutes time, resulting recovery of 84.74 % Th, 3.26 % U, 34,74 % RE, and 8.52 % PO4.

Precipitation condition and effect of volume fraction on corrosion properties of secondary phase on casted super-duplex stainless steel UNS S32750

Purpose The secondary phase decreased the corrosion resistance because of the segregation of Cr and Mo. Therefore, this paper aims to study the precipitation condition and the effect of secondary phase with volume fraction on corrosion behavior. Design/methodology/approach Secondary phase precipitated approximately from 375°C to 975°C because of saturated Cr and Mo at grain boundary by growth of austenite. Therefore, heat treatment from 800°C to 1,300°C was applied to start the precipitation of the secondary phase. Findings The secondary phase is precipitated at 1,020°C because of segregation by heterogeneous austenite. The growth of austenite at 1,000°C needs the time to saturate the Cr and Mo at grain boundary. When the volume fraction of austenite is 56 per cent (14 min at 1,000°C), the secondary phase is precipitated with grain boundary of austenite. The secondary phase increased the current density (corrosion rate) and decreased the passivation. That is checked to the critical pitting temperature (CPT) curves. The 1 per cent volume fraction of secondary phase decreased CPT to 60°C from 71°C. Research limitations/implications The precipitation of secondary phase not wants anyone. Casted super-duplex stainless steel (SDSS) of big size precipitates the secondary phase. This study worked the precipitation condition and the suppression conditions of secondary phase. Social implications Manufacturers need precipitation condition to make high-performance SDSS. Originality/value The corrosion resistance of SDSS is hard the optimization because SDSS is dual-phase stainless steel. The precipitation of the secondary phase must be controlled to optimize of the corrosion resistance of SDSS. Anyone not studied the precipitation condition of secondary phase and the effect of secondary phase with volume fraction on corrosion behavior of SDSS.

Modeling Seawater Intrusion to Coastal Aquifers in South Coast of Laizhou Bay, China

In this study, a two-dimensional SEAWAT 2000 model is developed to simulate the seawater intrusion to coastal aquifers and brine water/fresh water interaction in the south of Laizhou Bay, Shandong Province, China and forecast the seawater intrusion and brine water/freshwater interface development in the coming years. The model profile is perpendicular to the coastal line, about 40 km long and 110 m in depth, and consists of two interfaces, freshwater-saline water interface and brine water-saline water-seawater interface. The parameters of aquifers in the SEAWAT-2000 model are calibrated by trial-error method repeatedly to fit the head and salinity measurements. Based on the historical groundwater and brine water exploration and natural precipitation condition, the prediction results indicate that equivalent freshwater head in shallow freshwater-saline water area will decrease year by year and decline 2.0 m in the forecasting period, caused by groundwater over-pumping for irrigating farmlands. The groundwater head in the brine-saline water area will also decrease about 1.8 m in forecasting period. A larger depression cone appears in the brine area, with smaller funnels in other areas. The salinity in the brine area finally drops below 105g/l. In the meanwhile, the salinity increases in other areas, damage fresh groundwater resources.

The Decrasing Trend of Precipitation Observed at Watesheds in Padang for The Period 1975-2013

One of the consequences of the ongoing climate change is the increasing likelihood of extreme precipitation frequency in the future, which causes the declining trend of total precipitation that affects water debits in the watersheds and brings difficulties to a city like Padang that is situated near the watersheds. In order to elaborate on this, a number of extreme precipitation indices recommended by ETCCDMI was utilized to assess the extreme precipitation condition for the period 1975-2013. These indices were calculated based on the rain-gauge stations along the watersheds in and around Padang. Before processing the data, a series of homogeneity test were undertaken to make sure the data were comparable. The results showed that there was a significant declining trend on the total annual precipitation (PRCPTOT), an increasing trend of the number of days without rain (R0) and a decreasing frequency of the number of days with precipitation of more than 50 mm in the Batang Kuranji Watershed. The results suggested that atmospheric circulations, such as El Nino and positive Dipole Mode, have played their role on the trend as a result of their intensified frequency due to global warming.