Rong Zhihao, Tang Xincun, Wu Liping, Chen Xi, Dang Wei, Li Xing, Huang Liuchun, Wang Yang
College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, People's Republic of China.
R Soc Open Sci. 2020 Jan 22;7(1):191619. doi: 10.1098/rsos.191619. eCollection 2020 Jan.
In this study, we propose a growth pathway of scorodite in an atmospheric scorodite synthesis. Scorodite is a non-direct product, which is derived from the transformation of its precursor. Different precursor speciation leads to different crystallinity and morphology of synthesized scorodite. At 10 and 20 g l initial arsenic concentration, the precursor of scorodite is identified as ferrihydrite. At 10 g l initial arsenic concentration, low arsenic concentration is unfavourable to the complex between arsenate and ferrihydrite, inhibiting the transformation of ferrihydrite into scorodite. The synthesized scorodite is 1-3 µm in size. At 20 g l initial arsenic concentration, higher arsenic concentration favours the complex between arsenate and ferrihydrite. The transformation process is accessible. Large scorodite in the particle size of 5-20 µm with excellent crystallinity is obtained. However, the increasing initial arsenic concentration is not always a positive force for the growth of scorodite. When initial arsenic concentration increases to 30 g l, Fe(O,OH) octahedron preferentially connects to As(O,OH) tetrahedron to form or ion. Fe-As complex ions accumulate in solution. Once the supersaturation exceeds the critical value, the Fe-As complex ions deprotonate and form poorly crystalline ferric arsenate. Even poorly crystalline ferric arsenate can also transform to crystalline scorodite, its transformation process is much slower than ferrihydrite. Therefore, incomplete developed scorodite with poor crystallinity is obtained.
在本研究中，我们提出了常压合成臭葱石的生长途径。臭葱石不是直接产物，而是由其前驱体转化而来。不同的前驱体形态导致合成臭葱石的结晶度和形态不同。当初始砷浓度为10和20 g/L时，臭葱石的前驱体被确定为水铁矿。当初始砷浓度为10 g/L时，低砷浓度不利于砷酸盐与水铁矿之间的络合，抑制了水铁矿向臭葱石的转化。合成的臭葱石尺寸为1-3 µm。当初始砷浓度为20 g/L时，较高的砷浓度有利于砷酸盐与水铁矿之间的络合。转化过程是可行的。获得了粒径为5-20 µm、结晶度优异的大颗粒臭葱石。然而，初始砷浓度的增加对臭葱石的生长并不总是产生积极作用。当初始砷浓度增加到30 g/L时，Fe(O,OH)八面体优先与As(O,OH)四面体连接形成 或 离子。Fe-As络合离子在溶液中积累。一旦过饱和度超过临界值，Fe-As络合离子去质子化并形成结晶度差的砷酸铁。即使是结晶度差的砷酸铁也能转化为结晶臭葱石，但其转化过程比水铁矿慢得多。因此，得到的是结晶度差、发育不完全的臭葱石。
