L. Becze

The nature of synthetic basic ferric arsenate sulfate (Fe(AsO4)1−x(SO4)x(OH)x) and basic ferric sulfate (FeOHSO4): their crystallographic, molecular and electronic structure with applications in the environment and energy

In this study we investigate a new family of arsenate-bearing phases belonging to one set of structures (Basic Ferric Sulfate-BFS: monoclinic–orthorhombic FeOHSO4) that are significant as an industrial arsenic control material in the environment or a cathodic material in rechargeable Li-ion battery cells. We determine for the first time (after two decades of its known existence in the processing industry) the average crystallographic structure of Basic Ferric Arsenate Sulfate-BFAS: Fe(AsO4)1−x(SO4)x(OH)x·(1−x)H2O) that is a member of this family of phases and how it relates to its parent BFS structure. Moreover, we demonstrate how the substitution of AsO4 ↔ SO4 affects the crystallographic structure of these phases, the phase(s) that are formed and their material properties as environmentally stable arsenic controls or Li-ion battery cathodes.

The effect of copper on the precipitation of scorodite (FeAsO4·2H2O) under hydrothermal conditions: Evidence for a hydrated copper containing ferric arsenate sulfate-short lived intermediate

The effect of copper sulfate on scorodite precipitation and its mechanism of formation at 150 °C was investigated. Scorodite was determined to be the dominant phase formed under all conditions explored (0.61 < Fe(III)/As(V) < 1.87, 0.27-0.30 M Fe(SO(4))(1.5), 0-0.3 M CuSO(4), 0-0.3 M MgSO(4), at 2.5 h and 150 °C). The produced scorodite was found to incorporate up to 5% SO(4) and ≤1% Cu or Mg in its structure. The precipitation of scorodite was stoichiometric, i.e. the Fe/As molar ratio in the solids was equal to one independent of the starting Fe/As ratio in the solution. The presence of excess ferric sulfate in the initial solution (Fe/As>1) was found to slow down the ordering of the H-bond structure in scorodite. Precipitation under equimolar concentrations (As = Fe = Cu = 0.3 M), short times and lower temperatures (30-70 min and 90-130 °C) revealed the formation of a Cu-Fe-AsO(4)-SO(4)-H(2)O short lived gelatinous intermediate that closely resembled the basic ferric arsenate sulfate (BFAS) type of phase, before ultimately converting fully to the most stable scorodite phase (96 min and 138 °C). This phase transition has been traced throughout the reaction via elemental (ICP-AES, XPS), structural (PXRD, TEM) and molecular (ATR-IR, Raman) analysis. ATR-IR investigation of an arsenic containing industrial residue produced during pressure leaching of a copper concentrate (1 h and 150 °C) found evidence of the formation of an arsenate mineral form resembling the intermediate basic ferric arsenate sulfate phase.

Formation of Massive Gunningite-Jarosite Scale in an Industrial Zinc Pressure Leach Autoclave: A Characterization Study

Abstract Recent attempts to increase the throughput in an industrial zinc pressure leach autoclave resulted in massive scale formation not encountered previously. According to a comprehensive characterization study, the results of which are presented in this paper, in addition to jarosite and elemental sulphur that commonly form and report in the residue of this process, the scale samples contained significant amounts of the mineral gunningite (ZnSO4·H2O) plus minor amounts of szomolnokite (FeSO4·H2O). SEM-EDS examination of cross sections made from the reduced scale revealed gunningite which acted as a binder forming a matrix within which the natrojarosite lens-like particles were embedded. The presence of gunningite and the other major phases (natrojarosite, hematite, elemental sulphur and szomolnokite) were established unequivocally by applying vibrational (ATR-FTIR and Raman) spectroscopic analysis in additional to conventional XRD method. Finally the quantitative abundance of each of these phases was determined via the development of a 3-step extraction-dissolution procedure. According to this quantitative method, the composition of the bulk of the scale consisted of gunningite (23-55%), natrojarosite (13-37%), hematite (13-26%), elemental sulphur (3-10%), szomolnokite (3-7%) and sphalerite (0.7-3%).

Raman Spectroscopy in the Hydrometallurgical and Materials Engineering World

Autoclave processing of arsenical sulphide feedstocks from which precious metals (Cu, Co, Zn, Ni, Au) are extracted from employs high temperatures (150-225°C) which produces Fe-AsO4-SO4 crystalline phases [1-2]. In 1994, four phases were reported to form for the high temperature (150-225°C) Fe-AsO4-SO4 system [2] but confusion arose in 2007, as the discovery of two new phases were reported [3]. Therefore it was evident that these phases had not been fully identified in terms of arsenate speciation, in spite of the fact that some of these phases are used and advocated in arsenic disposal [2-3]. In the second case, attempts to increase the throughput (extraction of Zn) of an industrial leach autoclave, a massive scale formation never before observed resulted in halting of production. The final case deals with the binding mechanism between the highly commercialized N719 molecule and nano-crystalline anatase (TiO2) as a semiconductor in the DSSC field which has been highly investigated over the last decades [4-5] as a result of the high efficiencies they produce.