USE OF DOLOMITE AS A PHOSPHATE ADSORBENT IN WASTEWATER: COMPARATIVE EVALUATION BETWEEN NATURAL AND PURIFIED SAMPLES

Abstract

Eutrophication of water bodies, intensified by excess phosphorus from domestic effluents and agro-industrial activities, constitutes one of the greatest environmental challenges today. In this context, the search for low-cost and widely available adsorbent materials has been considered strategic to mitigate diffuse pollution. Dolomite, a carbonate mineral abundant in Brazil, has potential for phosphorus removal, but its efficiency depends on structural conditions and the presence of impurities. Therefore, this study comparatively evaluated the phosphorus adsorption efficiency of natural dolomite (ND) and purified dolomite (PD), integrating performance analyses in adsorption tests and structural and surface characterizations by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The calibration curve established for phosphorus determination showed linear behavior in the range of 1 to 25 mg L⁻¹. The limits of detection (LOD = 0.178 mg·L⁻¹) and quantification (LOQ = 0.593 mg·L⁻¹) confirmed the technique's sensitivity, allowing the monitoring of subtle variations after adsorption. In comparative tests, raw dolomite showed removals between 24.3% and 36.7%, with a tendency for efficiency to decrease at higher concentrations. Purified dolomite consistently performed better, with removals between 89.9% and 95.6%, regardless of the initial phosphate concentration. This difference was attributed to the elimination of impurities during purification, which resulted in greater surface area, porosity, and availability of Ca²⁺ and Mg²⁺ active sites. Characterization analyses reinforced the test results. FTIR confirmed the presence of typical carbonate bands (CO₃²⁻) in both samples, in addition to the emergence of new bands related to phosphate groups (PO₄³⁻) after the adsorption process, more intense in the purified dolomite. SEM images revealed that the DN had irregular, heterogeneous particles with fissures, while the DP presented homogeneous, compact particles with greater porosity. The EDS results confirmed the characteristic elemental composition of dolomite and, decisively, the presence of phosphorus only in the DP saturated at 40 mg L⁻¹, direct evidence of greater phosphate anion fixation efficiency. Comparison with the literature showed that the results of this study are consistent with studies reporting low efficiencies in untreated dolomite and removal rates greater than 90% in purified or modified materials. In this sense, purified dolomite demonstrated performance comparable to more expensive synthetic adsorbents, such as modified zeolites and metal oxides, standing out for its widespread availability and economic viability in Brazil. Thus, purified dolomite represents a promising, sustainable, and low-cost alternative for phosphorus removal from aqueous solutions, with potential application in decentralized sanitation systems.