Quartz sand is a common mineral that typically contains impurities such as feldspar. In order to improve the grade of quartz sand, flotation and other methods are used to remove feldspar impurities. The flotation principle for removing feldspar from quartz sand relies on exploiting the differences in surface properties between feldspar and quartz to achieve separation. Typically, during the flotation process, adjusting the pH value of the slurry and adding appropriate collectors and frothers can create different flotation properties for feldspar and quartz, thus achieving separation.
Here are three commonly used flotation methods for removing feldspar from quartz sand:
The hydrofluoric acid flotation method is a traditional approach for separating quartz and feldspar by adding an activator, hydrofluoric acid, or fluoride to the slurry. In a strong acidic medium, amine-type cationic collectors are used to preferentially float feldspar.
Operating Principle: With the addition of hydrofluoric acid to the slurry, the pH value of the slurry decreases, disrupting the dissociation equilibrium on the surfaces of quartz and feldspar. Electron reactions occur in the slurry, ultimately resulting in a certain electronegativity on the surface of feldspar. When cationic collectors are added to the slurry, they adsorb to the surface of feldspar, allowing feldspar to float preferentially due to hydrophobicity.
This flotation method utilizes a mixture of anionic collectors, amine, and petroleum sulfonate in a strongly acidic medium (pH 2-3) to preferentially float feldspar.
Operating Principle: After acid is added to the slurry, when the pH value of the slurry is between 2-3, quartz is at or near zero potential, and its surface is not charged. Since the pH value at which feldspar reaches zero potential is lower, feldspar itself is negatively charged when quartz is at zero potential. Therefore, when a mixture of anionic and cationic collectors is added to the slurry, quartz surfaces form weak electrostatic and molecular adsorption, while feldspar surfaces exhibit characteristic adsorption of active aluminum ions. Multiple adsorption mechanisms in the slurry promote and synergize, resulting in greater adsorption of collectors on the surface of feldspar than quartz, thus preferentially floating feldspar and achieving separation from quartz.
To optimize the quartz-feldspar flotation process and mitigate the corrosive effects of strong acids, it's essential to remove the influence of strong acids on the ore dressing environment. Under acidic-free conditions, two methods of flotation are employed: flotation in a neutral medium and flotation in an alkaline medium.
Operating Principle in a Neutral Medium: In a neutral medium, both quartz and feldspar carry negative charges. Anionic collectors adsorb on the surface of feldspar Al microareas, forming hydrophobic molecular clusters. At this point, the adsorption capacity of feldspar is much greater than quartz, allowing feldspar to be preferentially floated. Anionic collectors such as oleate anions and cationic collectors are used, and sodium hexametaphosphate inhibitors are added to suppress feldspar.
Operating Principle in an Alkaline Medium: In an alkaline medium, the floatability of feldspar weakens while that of quartz remains relatively unchanged, allowing quartz to be preferentially floated. When the pH value of the slurry is between 11-12, alkaline earth metal ions are added as activators and alkyl sulfonates as collectors. Quartz is then floated first, achieving separation from feldspar.
The above three flotation methods are commonly used in removing feldspar impurities from quartz sand. Different properties and mineral compositions of quartz ores require different flotation methods. It is recommended to conduct ore dressing tests before selecting the flotation method based on the test results to achieve the best results and ensure the purity improvement of quartz sand.
