Experimental study on treatment of middlings produced in gravitational separation of collophanite using flotation process and gravity separation plus flotation combined process

With the use of enhanced gravity separation method to separate out tailings from low-grade collophanite, only part of up-to-standard concentrate is obtained, and lots of middlings still with a higher grade are produced during the separation process. In order to get a higher recovery of concentrate, test on flotation of the middling is conducted based on result of analysis of its elementary and mineralogical compositions and dissemination of minerals. Through FTIR analysis of mechanism of reverse flotation process, a gravity separation + flotation combined process is developed based on the results of study on enhanced centrifugal gravity separation and flotation processes. As indicated by study results, the grade of P₂O₅ of gravity separated middling is 17.12%; the middling contains predominately apatite, dolomite and quartz; the finer sizes of the middling can get comparatively a better dissociation while some of the > 0.074 mm coarser particles still remain undissociated; in direct flotation of milled middling, the concentrate tends to gradually rise in grade and drop in yield with the increase of dosage of sodium carbonate, and the contrary is the case with the increase of dosage of collector ZF-1; the optimum dosages of sodium carbonate and ZF-1 are 3.0 kg/t and 1.5 kg/t, respectively, and in this case the yield and grade of concentrate are 67.81% and 21.41%, respectively; in reverse flotation of the middling, with the increase of dosage of sulfuric acid, the yield of concentrate tends to gradually decrease with its grade first going up and then maintaining stabilized; with the increase of dosage of collector ZF-2, the yield of concentrate gradually drops yet with a gradually declining rate while the grade of concentrate tends to first rise and then keep stabilized; in this case, the optimum dosages of the sulfuric acid and ZF-2 are 5 kg/t and 0.9 kg/t, respectively, with the yield and grade of concentrate being 60.49% and 26.97%, respectively. FTIR analysis shows that no obvious adsorption effect can be observed between ZF-2 and collophanite under optimal testing conditions, and the ZF-2 is seen to only adsorb onto surface of dolomite forming a good barrier for the \mathrmCO_3^2- of the dolomite itself, which can help achieve the objective of getting rid of carbonate minerals through reverse flotation process. Through the use of the gravity separation + flotation combined process, the yield and grades of final concentrate and tailing product are 39.06% and 25.12%, 60.94% and 8.51%, respectively, well demonstrating the effectiveness of the process.