Sand washing: remove iron impurities

Silica sand is an important industrial raw material and is widely used in ceramics, glass, refractory materials and other fields. The difference between silica sand and quartz sand lies in the content of silica. The main component of silica sand is quartz, and other impurities in silica sand will directly affect the quality of the product.

Iron in silica sand may be present in many forms, including hematite, magnetite, goethite, limonite, and pyrite, and may be present as individual particles or by surface contamination on sand particles. If the content of iron is too high, the use value of quartz sand will be greatly reduced. Here are several methods for removing iron in sand washing.

1. Magnetic separation method

      The premise of magnetic separation for iron removal is that the impurities are magnetic minerals, including strong magnetic minerals such as magnetite and weak magnetic minerals such as hematite and limonite. Compared with other methods, the cost of magnetic separation is lower, and it is mainly divided into wet magnetic separation and dry magnetic separation.

2. Pickling method

      When insoluble in acid, the reaction of iron and acid solution can generate a complex aqueous solution. It is mainly divided into cold acid treatment and hot acid treatment, but the chemical composition has a greater impact on the environment and the cost is relatively high.

3. Ultrasonic

      Ultrasound is a sound wave with a frequency higher than 20,000 Hz, which is widely used in gravel, cleaning, ranging and other fields. Ultrasonic iron removal is mainly used to remove thin film iron. Ultrasonic waves are introduced into the cleaning solution to create air pockets in the cleaning solution. Ultrasonic iron removal can not only remove impurities on the surface of minerals, but also remove impurities in the gaps. Ultrasonic iron removal is relatively expensive for silica sand, which is a relatively inexpensive raw material, but is still necessary for fields with high purity requirements and low production volumes.

4. Bioleaching

      Some research groups have experimented with Aspergillus niger strains to remove iron from silica sand, as these strains convert into citric acid, oxalic acid, etc. The resulting organic acids are then used as complexing agents for iron in silica sand. The experimental results show that, compared with industrial acids, organic acids can save nearly a quarter of the cost through fermentation, but due to limited conditions, they have not been used on a large scale.

5. Mechanical scrubbing

      Mechanical scrubbing is more common, mainly rod friction scrubbing and agitation scrubbing. Through the friction between the external force and the sand grains, the iron-containing substances attached to the surface are removed. The method has low cost and simple operation, but the iron removal rate is also low.