مقاله انگلیسی رایگان در مورد کاهش جذب کوارتز در شناور سازی زغال سنگ مرغوب – الزویر 2019

Flotation tests using artificial mixtures of clean coal and quartz were conducted with and without the presence of sodium hexametaphosphate (SHMP) to study the effect of polyaluminum chloride (PAC) on quartz entrainment in fine coal flotation. Comparisons of flotation results show that the degree of quartz entrainment was greatly reduced using a suitable amount (e.g., 20 mg/L) of PAC in the absence of SHMP, however, significant changes of PAC on quartz entrainment did not appear in the presence of SHMP. The possible mechanisms responsible for the reduced quartz entrainment using PAC in fine coal flotation were investigated by particle size distribution measurements, zeta potential measurements, and interaction force calculations. Analysis of particle size distribution results reveals that when SHMP was not added, quartz particles were selectively aggregated with the addition of 20 mg/L PAC and the aggregation of quartz or coal particles was negligible at a high PAC dosage (e.g., 50 mg/L). Meanwhile, the aggregation of quartz particles induced by PAC was eliminated with the presence of SHMP. The electrostatic double layer repulsive force between quartz particles was calculated using the Deyaguin-Landau-Verwey-Overbeek (DLVO) theory with incorporating the results of zeta potential measurements. At 20 mg/L of PAC, the negative surface charge of quartz particle was neutralized and the electrostatic double layer repulsive force between quartz particles reached the minimum. These findings might be reasons of the aggregation of quart particles and therefore reduce the quartz entrainment in fine coal flotation.

Introduction

Gangue entrainment is the main reason that results in the deterioration of flotation concentrate grade. The gangue entrainment problem in coal flotation has become more severe since the proportion of fine and ultrafine particles in coal flotation feed increases greatly with the popularization of mechanical mining and heavy medium cyclone separation technologies. Since China has adopted much stricter environmental regulations, the production of high quality clean coal has become a major challenge faced by the coal flotation industry today. Reducing the entrainment of fine and ultrafine gangue minerals seems to be a promising approach to improving the grade of clean coal, although, studies reported that it is very difficult to deal with [1–3]. In recent years, a number of studies have been conducted to improve the quality of flotation clean coal. Jiang et al. [4] and Peng et al. [5] applied inclined plates in the flotation column to increase the segregation rate between the rising bubbles and descending liquid by which both the capacity and the separation efficiency of the flotation column increased. Ni et al. [6] designed an unconventional flotation column by adopting the mechanism of gravity sedimentation into flotation. They found that the ash of clean coal obtained with the new column was reduced by 1.17% compared with the conventional flotation column. The successes in improving clean coal quality also have been achieved by the development of new compound collector to promote fine particle recovery [7], the uses of ultrasonic [8], and high intensity conditioning to realize surface cleaning [9]. Recently, two liquid flotation, for example the Hydrophobic-Hydrophilic Separation (HHS) technology, has been developed to remove the gangue minerals by dispersing coal in hydrocarbon phase [10,11]. The entrainment of gangue minerals such as quartz, kaolinite, and montmorillonite in fine coal flotation has been recognized since the beginning of employing flotation. However, research effort has been mainly focused on developing new processes to improve the clean coal quality as abovementioned. On the other hand, various studies have also been carried out to understand the gangue entrainment.