The effect of precursor speciation on the growth of scorodite in an atmospheric scorodite synthesis

Abstract

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 −1 initial arsenic concentration, the precursor of scorodite is identified as ferrihydrite. At 10 g l −1 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 −1 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 −1 , Fe(O,OH) 6 octahedron preferentially connects to As(O,OH) 4 tetrahedron to form Fe H 2 As O 4 2 + or FeHAs O 4 + 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.

First principles study of structural and electron properties in scorodite: the bulk and surface

“…18 were used to establish the initial scorodite crystal structure, which was extensively adopted in subsequent works. 5,13,25,26 Different from previous studies, the position of the H atom in the crystal structure has been discussed in ref. 18.…”

“…Due to its good crystallization and stability(dissolution process), scorodite is considered as an ideal material for arsenic fixation. 5,6 Being a secondary mineral, scorodite can be generated on the surface of arsenic-bearing minerals through weathering and precipitation. 7,8 Synthetic scorodite has been widely studied in the past few decades, but large particles of scorodite cannot be produced at present (the reported particle diameter is B1 mm).…”

“…Studies conducted thus far have shown that the Fe/As content ratio on the surface of scorodite is greater than 1. 5,20 In addition, under different synthesis conditions, the chemical states of O 1s on the surface of scorodite also exhibit significant differences. 5 These differences are mainly manifested in the relative contents of OH, H 2 O, and O 2 À .…”

“…5,20 In addition, under different synthesis conditions, the chemical states of O 1s on the surface of scorodite also exhibit significant differences. 5 These differences are mainly manifested in the relative contents of OH, H 2 O, and O 2 À . Therefore, it is of great significance to study the crystal structure and surface configuration of scorodite.…”

Stabilizing Arsenic in Copper Heap Leaching Residues

“…It should be noted that there is evidence that calcium arsenate compounds decompose upon contact with atmospheric CO 2 or carbonate ions to form calcium carbonate and a soluble arsenic acid [18]. The best alternative for arsenic stabilization is the formation of scorodite (FeAsO 4 •2H 2 O) [20][21][22], which is capable of containing between 20-25% of As [23] and is stable under oxidizing conditions in the pH range of 2.0-6.0 [18,24]. The formation of scorodite at atmospheric pressure requires strict rigor with respect to the pH.…”