- Antonio Clareti Pereira*
- PhD in Chemical Engineering São Paulo University – USP Belo Horizonte – MG – Brazil
- DOI: 10.5281/zenodo.20596981
Ferrous sulfate is produced in large quantities by
hydrometallurgical operations, steel pickling, titanium dioxide manufacturing,
acid regeneration circuits, and several wastewater treatment processes. Despite
numerous utilization routes, significant quantities remain underutilized or
require costly disposal and stabilization. This review critically evaluates an
integrated process concept for converting ferrous sulfate solutions into two
commercially valuable products: ammonium sulfate fertilizer and
powder-metallurgy iron. The first stage involves urea-assisted conversion of
dissolved ferrous sulfate into ammonium sulfate and ferrous carbonate.
Thermodynamic assessments indicate strongly favorable reaction equilibria
across typical process temperatures, and the low solubility of ferrous
carbonate promotes efficient iron recovery from solution. The second stage
involves thermal decomposition and hydrogen reduction of ferrous carbonate to
produce metallic iron powder. Available thermodynamic and kinetic studies
indicate that hydrogen reduction becomes increasingly favorable at moderate
temperatures and may provide a low-carbon alternative to conventional iron
powder production routes. The review compares existing ferrous sulfate
management strategies, discusses the chemistry of urea hydrolysis and siderite
precipitation, evaluates thermodynamic and process limitations, and examines
industrial opportunities associated with fertilizer and powder metallurgy
markets. Particular attention is given to reaction feasibility, process
integration, product quality requirements, and scale-up challenges. The
analysis suggests that the proposed dual-product pathway is a promising
circular economy strategy that can reduce environmental liabilities while
generating two independent revenue streams from a widely available industrial
residue.
