Quartz and feldspar are similar in physical properties, chemical composition, and structure, making flotation the main method for their separation. The flotation separation of quartz and feldspar is not only the key to silica sand beneficiation, but also the basis of flotation separation of silicate minerals.
Quartz and feldspar are similar in physical properties, chemical composition, and structure, making flotation the main method for their separation. The flotation separation of quartz and feldspar is not only the key to silica sand beneficiation, but also the basis of flotation separation of silicate minerals.
The traditional method of flotation separation of quartz-feldspar is the hydrofluoric acid method, which began in the 1940s, also known as the “fluorine and acid” method. In the presence of strong acid and fluoride ions, feldspar is preferentially flotated with cationic collectors. Because fluoride ion harms the environment, in the 1970s, Japan, the United States and other countries began to study the “fluorine-free” flotation method of silica sand. Under the condition of strong acid medium (sulfuric acid), the mixed collector of anion and cation was added to Japan Katayanagi to preferentially flotate feldspar to realize the flotation separation of quartz and feldspar. This method is commonly known as “sulfuric acid method” or “fluorine-free acid” method.
In order to further improve the quartz-feldspar flotation separation process and remove the impact of strong acid on the environment, Tang Jiaying et al. began to study a new process for flotation separation of quartz-feldspar with mixed anion and cation collectors since 1984, and it was successfully used in industry. Production. In this method, in a natural neutral medium, using the difference in the structural composition of quartz and feldspar, under unique process conditions, a mixed collector of anions and cations is reasonably prepared, and the feldspar is preferentially flotated to achieve the separation of the two. This method is called silica sand “fluorine-free and acid-free” flotation method. For the treatment of fine and ultrafine particles, the magnetic carrier process has also attracted extensive attention in recent years. The separation of chalcocite and quartz, sphalerite and gangue, and coal and ash have been reported by magnetic carrier technology.
2 Crystal structure and surface properties of quartz and feldspar
Quartz and feldspar are both framework silicate minerals, they have the same crystal structure: silicon (aluminum) oxygen tetrahedra and four silicon-oxygen tetrahedra are connected with each other to form a framework that extends infinitely in three-dimensional space. structure. The charging mechanism of the two in the aqueous solution is basically the same: after the minerals are broken, the crystal is broken, the silicon (aluminum) oxygen bond is broken, the ions are adsorbed and positioned in the aqueous solution, and the surface of the hydroxyl group is generated. separation or adsorption to form different surface potentials.
Due to the high degree of polarization and strong hydrophilicity on the fractured section of the mineral, quartz and feldspar exhibit electronegativity in a wide pH range, and the zero electric point is very low. Due to the substitution of aluminum oxide tetrahedron to silicon oxide tetrahedron in the feldspar structure, there are subtle differences between the two in many aspects: Al3+ and Si4+ have different electricity prices. In order to compensate for the electricity price imbalance caused by the substitution of Al3+ for Si4+, And the introduction of alkaline earth metal ions such as K+, Na+, etc., the ionic bond between these metal ions and O2- is weak, the bonding force is weak, and it is easy to dissociate in water, leaving a negatively charged lattice on the surface of the mineral, which makes the usual situation The zero electric point of feldspar is lower than that of quartz. At the same time, since the Al-O bond is weaker than the Si-O bond, the bond is easier to break when broken, which exposes a large number of Al3+ chemically active areas on the surface of the feldspar. These differences lead to slightly different floatability of quartz feldspar, which provides the basis for the flotation separation of quartz and feldspar.
The most mature scheme for the flotation separation of quartz and feldspar is the HF acid scheme, but due to environmental problems and many inconveniences in the use of HF acid, many beneficiation workers are actively studying the fluorine-free separation scheme, which also represents The leading research direction of quartz-feldspar flotation separation. Among the above several quartz-feldspar fluorine-free flotation separation processes, the most mature and widely used is the acid pumice method, but this process requires strong acid medium conditions, resulting in serious equipment corrosion. Therefore, the neutral pumice method and several other process methods have good application prospects and represent the future development direction of the quartz-feldspar flotation separation process. Although these methods are not very mature at present, most of them are only laboratory results. , There are few examples of practical application in industrial production, but these process methods deserve further discussion and improvement, in order to realize industrial application at an early date.