Environmentally friendly separation of monazite and fluorite using carboxymethyl cellulose and octyl hydroxamic acid: Experimental and DFT calculations

Abstract

Fluorite, as the predominant calcium-bearing vein mineral in monazite-containing ores, presents significant challenges in selective separation due to its similar surface properties to monazite. This study demonstrates that carboxymethyl cellulose (CMC) effectively inhibits fluorite while allowing selective flotation of monazite using the biodegradable collector octyl hydroxamic acid (OHA). Micro-flotation tests revealed a remarkable recovery difference of 92.31 % between monazite and fluorite in single-mineral systems. Specifically, under the proposed reagent scheme (OHA as collector and CMC as depressant), the flotation recoveries of monazite and fluorite were 95.40 % and 3.09 %, respectively. In contrast, using a conventional reagent system (mixed collector of OHA and OP10, with EDTA as depressant), the recoveries of monazite and fluorite were 80.01 % and 29.51 %, respectively, with a flotation recovery difference of only 50.50 %. Artificial mixed-mineral tests under optimized conditions achieved a monazite concentrate grading 61.15 % rare earth oxides (REO) with 87.69 % recovery. Characterizations via contact angle measurements, zeta potential analysis, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and density functional theory (DFT) calculations confirmed strong preferential adsorption of CMC on fluorite surfaces via Ca-O bonding. This adsorption mechanism effectively prevents OHA attachment on fluorite while maintaining monazite’s floatability. This work provides insights into the efficiency and environmentally benign separation of monazite from fluorite (calcium-bearing vein materials).