Ramp rate-controlled mineralogical evolution and multi-scale structure–property framework for arsenate removal in nanohematite-bearing clay ceramic water filters

Abstract

Sintering kinetics govern phase evolution and structure–property relationships in clay-based ceramics, yet the influence of heating rate on mineralogical evolution and filtration performance remains poorly understood. Here, ferruginous clay ceramic water filters were used to develop a multi-scale process–structure–property framework linking sintering ramp rate to mineralogical restructuring, hematite crystallographic evolution, transport behaviour, and arsenate removal. The raw clay contained high Fe₂O₃ (28.22wt.%) and an intrinsic nanohematite phase (RHPA = 18.26%, D = 12.43nm), providing an in-situ iron oxide phase relevant to arsenate adsorption. Ramp rate regulated hematite abundance and crystallographic characteristics, while multi-criteria optimisation integrating porosity, transport performance, densification, structural integrity, and hematite reactivity identified an optimum ramp rate of 4 ◦Cmin⁻¹. Under these conditions, arsenate concentrations were reduced from 22.70 ± 1.50to9.91 ± 0.34µg L⁻¹ (56.3% removal), achieving compliance with WHO guidelines. Zeta potential measurements revealed a transition from a strongly negative surface charge in the raw clay ( − 32.1 ± 1.4mV) to a near-neutral charge in the optimised filter ( + 1.3 ± 0.2mV), consistent with arsenate adsorption occurring predominantly through inner-sphere interactions on hematite-bearing surfaces. The optimised filter retained 92.9 ± 2.6% of its flexural strength after prolonged aqueous exposure, indicating good structural stability. These findings establish sintering ramp rate as a key design parameter governing the evolution and performance of ferruginous ceramic filtration materials.