What are black impurities？

The black impurities in quartz sand may come from mechanical iron left in quartz sand after crushing by crusher, carbonized impurities and black mica, tourmaline, etc., which are accompanied in quartz ore.

01 Mechanical iron: 

the so-called mechanical iron, refers to the quartz sand in the process of beneficiation, crushing processing, semi-finished products mixed with variable 

content of foreign iron.

02 Charred impurities: 

Charred impurities are accidentally mixed in during quartz ore mining or processing, such as the perimeter of the yard is not cleaned, weed debris or dust, etc. 

are mixed into thequartz ore pile. After acid washing and other treatments, these impurities have been removed a lot by rinsing and other links, and the 

remaining impurities generally appear black.

03 Mica group minerals: 

Black mica is one of the associated minerals of quartz ore. Because the mica contains different material components, it will show different colors, and the 

common colors include red-brown, dark brown and even black. During pickling, it cannot be completely dissolved and decolorized by the acid, and part of 

the black mica remains in the quartz sand. Therefore, we can see the black mica impurities in quartz sand.

04 Tourmaline family minerals:

Tourmaline is one of the associated minerals of quartz ore. Tourmaline is a silicate mineral formed by weathering and is acid and alkali resistant, weakly 

magnetic or non-magnetic. Tourmaline color varies with the cation composition is often black, rose, dark blue, dark green, etc.. In acid washing can not be 

completely dissolved by the acid,if black tourmaline, in the quartz sand as black impurities.

Sources of black impurities

There are two main sources of black impurities in quartz sand, one is the companion of quartz ore, and the other is the black impurities mixed in from outside.

01 Quartz ore itself minerals: quartz ore itself companion is mainly the above-mentioned mica group minerals, tourmaline group minerals, minerals after weathering 

and other factors and quartz ore together.

02 Mixed in the black impurities: mechanical iron from the beneficiation equipment as well as auxiliary equipment, in the beneficiation equipment, mechanical iron 

mainly from the crusher grinding equipment, especially grinding equipment is the main source of iron in these devices to the normal wear and tear of equipment in 

the beneficiation, equipment generated by its own oxidation; and auxiliary equipment in the iron is mainly generated by the oxidation and rusting of equipment.

In addition, carbonized impurities are also inadvertently mixed in the quartz ore processing process.

Effect of black impurities on the quality of quartz sand

01 The influence of mechanical iron on the quality of quartz sand: If the quartz sand contains too much mechanical iron, it will also cause the oxidation reaction of the 

residual mechanical iron in the leaching process or drying process after pickling, causing the yellowing of quartz sand; it will consume more effective substances of 

acid in the pickling process, affecting the recycling effect of the subsequent recovery acid and causing the waste of acid.

02 The influence of other black impurities on the quality of quartz sand: If the black impurities in quartz sand cannot be completely removed by pickling, too many black 

impurities in quartz sand after pickling will affect the overall quality of quartz sand, reduce the selling price of quartz sand and increase the cost of subsequent processing.

Summary

Quartz sand enterprises want to control the black impurities within a certain range, the general practice of the industry has two aspects.

First of all, the quartz sand raw materials are controlled, such as quartz sand mining enterprises flotation and magnetic separation of quartz sand to remove most of the 

black impurities. Flotation can remove mica, feldspar, iron-bearing mineral impurities, etc. from quartz sand; magnetic separation can effectively remove a large amount 

of mechanical iron.

At the same time, quartz sand enterprises in the quartz sand processing process to control the mixing of black impurities, acid washing can not completely remove the 

black impurities need to use the color sorter to remove them.