# Eco-Friendly and Easily Synthesized Amorphous Fe–Ca (Oxy)hydroxide for Selective Phosphate Removal from Synthetic and Real Effluents: Synthesis, Optimization, and Application

## TL;DR

A new eco-friendly material called CaFe was developed to efficiently and selectively remove phosphate from polluted water, showing promise for preventing eutrophication.

## Contribution

The study introduces a novel amorphous Fe–Ca (oxy)hydroxide material optimized for selective phosphate adsorption with high efficiency and sustainability.

## Key findings

- CaFe achieved 84.86% phosphate removal from real effluent at pH 4 with a dosage of 1.5 g/L.
- The material demonstrated high selectivity for phosphate even in the presence of competing anions.
- Adsorption was spontaneous and endothermic with a maximum capacity of 41 mg/g at 30 °C.

## Abstract

The contamination of surface and groundwater by nutrients
due to
the discharge of untreated effluents is a serious environmental issue,
as it can promote eutrophication and compromise water quality. This
study aimed to optimize the synthesis of Fe–Ca (oxy)­hydroxide
(CaFe) and evaluate its adsorptive capacity for phosphate ions. The
coprecipitation route was chosen for the material synthesis. Structural
characterizations revealed that the material exhibits high roughness,
a large number of active sites, thermal stability, and a predominance
of the amorphous phase, all of which favor its efficiency in phosphate
adsorption. Optimization using response surface methodology (RSM)
yielded a high adjusted coefficient of determination (R
adj
2 = 0.97), indicating excellent fit to the
experimental data. The adsorption process followed the pseudo-second-order
kinetic model (R
adj
2 > 0.99)
and was best described by the Sips isotherm (R
adj
2 > 0.99), suggesting multilayer adsorption
in
a heterogeneous system. The maximum adsorption capacity (q
m = 41 mg/g) was achieved when the process temperature
was adjusted to 30 °C. Thermodynamic parameters confirmed that
the adsorption is spontaneous and endothermic (ΔH° = 17.38 kJ/mol). CaFe exhibits a high capacity for phosphate
adsorption, even in the presence of other anions, demonstrating excellent
selectivity and robustness in complex aqueous matrices. Moreover,
CaFe was capable of removing up to 84.86% of phosphate from a real
effluent sample by simply applying a dosage of 1.5 g/L and adjusting
the effluent pH (pH = 4). In conclusion, the results demonstrated
that CaFe is a promising material for phosphate removal, showing high
potential for application in the treatment of water bodies susceptible
to eutrophication. The findings indicated that CaFe exhibits excellent
performance as an adsorbent, with high adsorption capacity, strong
selectivity in the presence of competing anions, and satisfactory
regeneration efficiency. Additionally, the development of sustainable
materials such as CaFe is essential for achieving the Sustainable
Development Goals (SDGs), particularly SDG 6, SDG 9, SDG 12, and SDG
14.