High-purity quartz sand is a strategic resource urgently needed by the country. With the depletion of natural high-quality quartz deposits and the shortage of high-purity quartz sand, it is of great significance to actively explore the purification and processing technology of quartz sand. However, feldspar and quartz have similar surface properties, and their separation technology has always been a hot and difficult point in the field of mineral processing.
Difficulties in separating feldspar and quartz
Both feldspar and quartz are framework silicate minerals with very similar crystal structures. If 1/4 of Si4+ in the quartz structure is replaced by Al3+, it is feldspar. It is the similar crystal structure and similar chemical composition that make feldspar and quartz similar in physical and chemical properties such as density and hardness, and it is difficult to separate them by methods such as gravity separation, magnetic separation, scrubbing, and grading.
At present, the most effective method for separating quartz and feldspar is flotation. The mechanism is based on the difference in the surface properties of feldspar and quartz. Under suitable flotation conditions, a single cation collector or an anion-cation combination collector is added. , to achieve the separation of feldspar and quartz. However, the similar crystal structure and chemical composition of the two make the charge type and charge amount of feldspar and quartz basically the same, resulting in no choice for the adsorption of cationic collectors such as amines, which are mainly electrostatic adsorption, on feldspar and quartz. sex. Cationic collectors such as amines can also collect quartz while collecting feldspar, and the flotation separation of the two is difficult.
Since the 1940s, expanding the surface properties of feldspar and quartz has become a hot and difficult point of research, and many researchers have been engaged in this research and have achieved remarkable results. Such as adjusting the pH value of pulp, changing the type of collector, changing the type of inhibitor and activator, surface pretreatment, etc.
Research progress on flotation separation technology of feldspar and quartz
Hydrofluoric acid method
The hydrofluoric acid method is a traditional method for separating quartz from feldspar. Hydrofluoric acid solution is a strong acid solution, which can be used as a pH adjuster in flotation pulp, and also as an activator for feldspar, and an amine collector (cationic collector) is used. Feldspar is preferentially flotated from the slurry, thereby realizing the flotation separation of quartz and feldspar.
Because HF is highly toxic, it causes serious harm to the environment and human health. In addition, it also corrodes production equipment, which has been gradually eliminated.
Fluorine-free and acid method
The fluorine-free and acid method refers to using strong acid as a modifier and adjusting the pH of the pulp to 2 to 3 without adding hydrofluoric acid, and using a single amine collector or an anion-cation combination collector to preferentially float Feldspar, so as to realize the flotation separation method of feldspar and quartz. The separation principle is mainly based on the difference of Zeta potential of feldspar and quartz, adjusting the pH to near the zero electric point of quartz with strong acid, that is, the quartz surface is not charged at this time, and the feldspar surface is negatively charged. The feldspar floats up and separates.
In comparison, the “hydrofluoric acid method” and the “fluorine-free and acid-based method” have similarities and differences. The common point is that both methods need to be carried out under the condition of strong acid medium. The difference is: the traditional “hydrofluoric acid method” has better flotation effect on minerals. When hydrogen ions change the surface potential of minerals, fluoride ions will also destroy the Si-O bonds of minerals, making the surface of feldspar appear more Al3+(s) region, thereby improving the surface activity of feldspar; however, when using the “fluorine-free and acid method” to flotate minerals, the Al3+(s) region has poor activity, and only a single collector cannot achieve the flotation effect. It is necessary to use a combination of mixed collectors to achieve the effect of flotation.
However, the fluorine-free and acid-containing method is still used for sorting under strong acid conditions, which has serious problems of equipment corrosion. At the same time, the treatment of acid-containing wastewater is also a major problem in industrial production. Therefore, the fluorine-free and acid-free method has become the focus of current research by researchers.
Fluorine-free and acid-free method
Fluorine-free and acid-free method, that is, without adding fluoride and acid, and adding single or anion-cation combination collectors in a neutral, weakly alkaline or strongly alkaline slurry system to separate feldspar and quartz by flotation.
Dai Qiang et al. summarized the mechanism of neutral flotation separation of feldspar and quartz in detail: in neutral medium, the surfaces of feldspar and quartz are both negatively charged, and at this time, Al3+(s) will be formed on the surface of feldspar, anionic surfactants On the surface of feldspar, characteristic localization adsorption will be formed, and then the addition of cations will combine with anion collectors to form a hydrophobic layer, which will strengthen the localization adsorption of anions and form a hydrophobic layer on the surface of feldspar. There is no localized adsorption of anions, and the adsorption capacity of the active agent on the quartz surface is weak, so the two can be separated.
The mechanism of the alkaline flotation quartz method: the added metal cations and anion collectors will react under alkaline conditions to form neutral complexes, and these complexes are the reason why quartz floats out of the pulp preferentially. Under the condition of high alkaline medium, feldspar will form a hydration layer on the surface, which will block the adsorption of external cations to the surface of feldspar.
At present, there is no unified and detailed mechanism explanation for the research of fluorine-free and acid-free method. The difficulties and hotspots of the research mainly focus on the design and development of anionic and cationic combined collectors, the development of regulators, and the activation of metal ions.
Other methods
In recent years, many researchers have proposed that other methods (such as scrubbing, microwave technology, calcined water quenching technology, ultrasound, etc.) can be used to expand the floatability difference between feldspar and quartz to enhance the separation effect of feldspar and quartz. For example, Yuan et al. studied the effect of ultrasonic wave on quartz sand flotation. In the case of a single mineral, ultrasonic treatment can promote the floating of calcite and barite, but inhibit the floating of quartz. The surface of the quartz is chemical adsorption, and the quartz surface is physical adsorption. Under the action of ultrasonic waves, the collector will fall off the surface of the quartz, thereby promoting the separation of quartz and inclusions; Huang Jie et al. studied the effect of calcination on quartz and feldspar. The results show that calcination can enlarge the flotation difference between quartz and feldspar. These methods provide some new ideas, but also require a longer research cycle.
Summary
Selecting neutral and alkaline pulp conditions for flotation separation of quartz and feldspar has good application prospects, and also represents the development direction of quartz-feldspar flotation separation technology. In the flotation process, the selection of flotation reagents, the concentration of pulp, the pH value of pulp, and the particle size of quartz will all affect the effect of flotation. Searching for agents that enhance the Al3+ activity on the feldspar surface or with strong binding ability, and various studies to promote the localization and adsorption of the agents on the feldspar surface are still the top priority.