Remarkable Effect of Sugar Waste Pyrolysis Oil as a Calcite Collector for Enhanced Phosphate Beneficiation via Reverse Flotation

Abstract

This study evaluates the effectiveness of pyrolysis oils, derived from key waste byproducts of the sugar industry, as collectors in the flotation of calcite, using phosphoric acid (PA) as depressant. The chemical structure of pyrolysis oil collectors (POCs) was analyzed using FTIR, GC-MS, and surface tension measurements, revealing a complex mixture of various molecular groups, including hydroxyl, carboxylic, aromatic, and alkane. The collecting effect of POC in calcite flotation was assessed through microflotation using an experimental setup based on Box–Behnken design (BBD). The findings revealed that, with an air flow rate of 0.9 L/min, a specific consumption of 95–99 mg/g, and a pH 6–7, the recovery rate of calcite achieved 88%. To validate the collector’s performances further, bench-scale flotation experiments revealed an enrichment of phosphate ore to 68.74 and 69.44% Bone Phosphate of Lime (BPL). The comprehensive multimodal characterization revealed distinct topographical changes in the calcite surface morphology, observed via AFM. This was followed by characteristic peak shifts in the Raman spectra, indicative of molecular-level interactions. Concurrently, the zeta potential measurements showed significant decreases to −22.32 and −20.95 mV for both POCs, corresponding to a notable enhancement in surface wettability. As a result, carboxylic acids, hydroxyls, and ester molecules were initially found to bind to Ca²⁺ sites on the lattice layer of the calcite surface, followed by the coadsorption of aromatics and hydrocarbon chains via hydrophobic interactions.