Combined with the previous background of processing technology and performance differences between the two types of kaolin, you can quickly identify them through the following methods:
Appearance and Physical Property Identification
Color & State: Ordinary kaolin is mostly natural white or light gray powder, retaining the fine texture of raw clay. High-activity kaolin has a higher whiteness after calcination, some of which is light off-white due to raw material differences, and the powder is more fluffy.
Water Immersion Test: Ordinary kaolin, as a raw clay mineral, will absorb water and expand obviously after being soaked, forming plastic mud. High-activity kaolin loses bound water after calcination, hardly expands after soaking, and has no obvious plasticity.
Chemical Activity Identification
Pozzolanic Reaction Test: Mix equal amounts of samples with calcium hydroxide (slaked lime) and water respectively, and test the strength after curing for 7 days. High-activity kaolin will undergo pozzolanic reaction to form cementitious products, and the test block has obvious hardness. Ordinary kaolin does not react, and the test block is loose and has no strength.
TG-DTA Analysis: Ordinary kaolin has an obvious endothermic peak of dehydration in the range of 500~600℃, corresponding to the dehydroxylation of layered structure. High-activity kaolin has completed dehydration, and there is no obvious endothermic peak in this temperature range.
Professional Index Detection
Loss on Ignition Test: The loss on ignition of ordinary kaolin is usually 12%~15%, while that of high-activity kaolin after calcination is generally less than 3%.
Activity Index Detection: Referring to the standard GB/T 18736-2017, the 7-day activity index of high-activity kaolin can reach more than 90%, while that of ordinary kaolin is less than 30%.
Simple On-site Identification
Ordinary kaolin has no obvious reaction with dilute hydrochloric acid, and can be kneaded into strips after soaking. High-activity kaolin cannot be kneaded into plastic mud strips. After mixing with calcium hydroxide generated by cement hydration, it can quickly increase the viscosity of the system, while ordinary kaolin does not have this phenomenon.