SiO2 in different databases

[Aksenova]

Hello!
Please tell me what does SiO2 (am-gel) and SiO2 (am-ppt) mean in the minteq4v.date database?
How do you decode am-ppt? ppt exactly?

[dlparkhurst]

They are derived from measurements of the solubility of amorphous silica phases.

There is not right answer about which one to use. Silica forms a range of solids from very soluble (gel or amorphous) to highly crystalline (quartz). They have varying degrees of hydration and crystallinity. The amorphous phases are likely to form first at high Si(aq) concentrations, but will then dehydrate and become more crystalline and less soluble with time. Thermodynamically, quartz is usually the most stable phase.

[Zhilei]

Dear,

A follow-up question: What is ppt meaning? For example, FeS(ppt). The user guide mentioned that it is "parts per thousand". If so, why do we add (ppt) after FeS or SiO2 here?

Thank you in advance,
Zhilei

[dlparkhurst]

No, it is short for precipitate. It implies a quickly precipitated solid that is likely to recrystallize to more stable forms with time.