1 Reasons for the yellowing of quartz sand pickling
Various acids commonly used in quartz sand pickling include hydrochloric acid, sulfuric acid, oxalic acid, hydrofluoric acid and the like. The crushing before pickling is often carried out by wet crushing, and some of them are broken by mechanical methods such as hammer breaking, so that the broken material contains a large amount of mechanical iron . Mechanical iron and quartz sand react slowly in water, and after a few days, mechanical iron will oxidize to trivalent iron to turn reddish yellow. Iron is oxidized faster in bare air if soaked with acid.
The first is that there is no magnetic separation process before partial pickling of quartz sand, and the mechanical iron is removed before pickling. After pickling, some of the mechanical iron remains in the quartz sand, and the mechanical iron is rapidly oxidized, contaminating the quartz sand. Causes the quartz sand to turn yellow directly.
The second is that the pickling is not complete, and the surface acid remains on the surface of the quartz particles, which also causes yellowing. Causes chloride ions, sulfur ions, etc. on the surface of quartz sand.
The third is that the quartz sand is not contaminated by contact with the handling tool before drying, causing secondary pollution (oxidation with iron) and yellowing.
Before pickling
After pickling
2 pickling standard process
Quartz sand crushing - washing - magnetic separation - acid leaching - washing - dehydration - drying
After the quartz sand is broken and washed with water, some impurities can be removed. Magnetic separation can remove more than 99% of mechanical iron. Acid leaching can add various acids according to the actual situation. Acid leaching equipment must be resistant to acid and alkali plastic containers. Stainless steel is not recommended. Partial acid corrosion of stainless steel. Acid immersion If possible, use a reactor or a heated, stirred vessel. Make the acid leaching more thorough and the reaction is more complete. Washing is also done with water, and cleaning is thorough.
3 preventive measures
1, crushing equipment
The selection must be mechanical iron that can be removed by magnetic separation. Some super-hard alloy wear-resistant, but not magnetized, can not be removed. Pickling is not possible to remove complete at a given time.
2, handling tools
It is best to use a conveyor belt, pump, or non-iron tool for handling tools. It is strictly forbidden to use a forklift before breaking. The forklift is prone to secondary pollution.
3, magnetic separation
There are many mechanical irons produced by mechanical crushing, and it is best to use automatic magnetic separation equipment . The number of magnetic grips or magnetic blocks of magnetic separation equipment such as artificial chutes should be sufficient and diligently cleaned. If necessary, check the effect of magnetic separation.
4, acid dip
The reaction kettle type is equipped with a stirring device to perform acid corrosion treatment, and the plastic container is immersed in a static soaking time and acid concentration ratio.
5, cleaning
The cleaning is cleaned with a mixing tank that can be stainless steel or plastic. Water enters from the bottom of the washing tub and water overflows from the surface of the washing tub. This cleaning effect is best and fast, ensuring that each quartz sand particle is cleaned.
6, drying
After washing, it should be dehydrated immediately and dried.
Quartz sand yellowing is again stressed by the secondary pollution of mechanical iron oxidation reaction, acid is not cleaned and caused by oxidation reaction with the vessel wall during container or drying.
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