Dolomite used in phosphate water treatment: Desorption processes, recovery, reuse and final disposition

Desorption is a method that contributes to two important aspects for the sustainability of the water treatments that involve adsorption processes: a) the regeneration of the adsorbent making it reusable in several efficient cycles and, b) the recovery of the adsorbate. In previous studies, it was shown that dolomite constituted an efficient adsorbent of phosphates from aqueous solutions. Once the adsorbent saturation is achieved, it becomes useless for further uses, generating waste, a new environmental problem if it could not be properly disposed. In this work, the main objectives were to study the phosphate desorption process for the recovery and reuse of dolomite and to evaluate the possibilities of a final disposal of exhausted dolomite for agricultural soil improvement and applying the desorbed phosphate as fertilizer. The most efficient agent for the desorption process was 1 M NH₄Cl. Ultrasound evidenced a negative effect on desorption. The pseudo-second order model fitted better the experimental data and the equilibrium time was 30 min. Up to four efficient adsorption-desorption cycles were obtained. Phosphate bioavailability of exhausted dolomite was assessed with autochthonous microorganisms. The obtained extracts were used in Lactuca sativa growth experiments, establishing that they are not phytotoxic and otherwise, could promote the vegetal growth.