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Published in James G. Speight, Handbook of Petrochemical Processes, 2019
High-purity industrial routes include a path through magnesium bicarbonate which can be formed by combining a slurry of magnesium hydroxide and carbon dioxide at high pressure and moderate temperature. The bicarbonate is then vacuum dried, causing it to lose carbon dioxide and a molecule of water: Mg(OH)2+2CO2→Mg(HCO3)2Mg(HCO3)2→MgCO3+CO2+H2O
Clean metallurgy and technical progress of light rare earth minerals
Published in Canadian Metallurgical Quarterly, 2023
Qiao Shule, Bian Xue, Cui Jianguo, Cen Peng, Wu Wenyuan
Beijing Nonferrous Metals Research Institute has developed a new process for the smelting and separation of Baotou rare earth ore by the magnesium bicarbonate method. The main process was shown in Figure 3. Taking advantage of the good solubility of magnesium bicarbonate, it was applied to the link of water leach solution debinding and extractant saponification respectively, which strengthened the solid–liquid reaction. In the extraction process, magnesium bicarbonate was used to saponify the extractant, and calcium hydroxide was added to the saponified wastewater to form calcium sulphate (reactions (1) and (2)) to remove sulphate from the wastewater, after which the CO2 generated from the water leach solution removal and extraction process was passed into the magnesium-containing wastewater to reform magnesium bicarbonate (reactions (3)–(5)), further reusing magnesium bicarbonate [35,36]. The recovery rate of rare earth has reached over 97%, realising the recycling of magnesium and CO2, zero discharge of ammonia nitrogen and wastewater, and greatly reducing the production cost. At present, Gansu Rare Earth New Materials Co., Ltd. has used this technology to establish a 30,000 t/a rare earth concentrate treatment line and achieves good results.
Mechanism, prevention and remedy of alkali-pumping in new constructed asphalt pavement
Published in International Journal of Pavement Engineering, 2021
Weixiong Li, Duanyi Wang, Chunlong Xiong, Jiangmiao Yu, Bo Chen, Xianshu Yu
One mechanism is referred to as ‘flowing’ alkali-pumping and is illustrated in Figure 4. During the construction of asphalt pavements, if the flow of alkaline materials from the lower synchronous gravel seal and subsidiary structure becomes uncontrolled due to the insufficient stirring of the asphalt mixture, the alkaline substances can easily dissolve in water. Typically, calcium oxide reacts with water to form water-insoluble calcium hydroxide (Equation (2)). During paving, high temperatures develop, and magnesium oxide reacts with water forming magnesium hydroxide, which induces water solubility (Equation (3)). Then, when the water flowing into the pavement structure in the gravel seal and the subsidiary structure is in contact with the high-temperature mixture, part of the magnesium bicarbonate might decompose to form magnesium carbonate (Equation (4)).
Evaluation of spatio-temporal variations in water quality and suitability of an ecologically critical urban river employing water quality index and multivariate statistical approaches: A study on Shitalakhya river, Bangladesh
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Md. Humayun Kabir, Tanmoy Roy Tusher, Md. Saddam Hossain, Md. Sirajul Islam, Rifat Shahid Shammi, Tapos Kormoker, Ram Proshad, Maksudul Islam
Total dissolved solids (TDS) represents the total amount of dissolved solids such as sodium, calcium, magnesium, bicarbonate, chloride contents in water (Parveen et al. 2017). The average TDS contents was found to be in the range of 520.58–607 mg/L (Table 2), which was within the prescribed level of 500 mg/L according to WHO (2011). All the sampling sites showed high TDS values during post-monsoon period as low water level increases the concentration TDS in the river (Table 2). Higher contents of TDS in post-monsoon could be attributed to the dissolution of salts from agricultural surfeit and industrial discharge because of anthropogenic activities alongside the river (Jindal and Sharma 2010). Islam et al. (2012b) observed that the TDS contents in the Dhaleshwari river water were ranged from 190–224, 69–131, and 95–299 mg/L in pre-monsoon, monsoon, and post-monsoon season, respectively. Analogous results were also documented by Islam et al. (2017) who found that the TDS contents ranged from 653.6–632 mg/L in the Karnaphuli river water (Table 3).