Question from a humble farmer. What is K2O-nSiO2-xH2O?

Question

In need of K2SiO3 for my cucumber plants, I purchased a bag of potassium silicate. The molecular formula is K2O-nSiO2-xH20. Normally, my bags of fertilizer are easy to figure out. For example, Ca(No3)2, or calcium nitrate, has a molecular weight of 164.0878 g/mol. The purity is also 95%. Knowing the purity and the molecular weight, I normally can find out how many ppm of Ca or N I want to use in my hydroponic nutrient tank. With K20-nSiO2-xH20, I don't understand 'n' and 'x.' I've googled this only to be stumped. I just don't get it.

 

The bag of fertilizer (K2O-nSiO2-xH2O) has the following information listed on it:

Wt% K2O 26.5~29.5

Wt% SiO2 55~60

Weight ratio (SiO2/K2O) 2.0~2.2

Mole ratio (SiO2/K2O) 3.2~3.4

Bulk Density g/L 400~600

solid % 82~89

particle size 270+/-50

purity 77%

 

Please help me better understand this. I need to know the molecular weight, so I can figure out how many ppm of Si and K to add to the solution. Thank you for any help. 

 

Farmer Josh

Answer 1

The n represents the "number" of silicon dioxides that have been polymerized, and the x is the moles of water of hydration. The reason it is x and not a defined number is because it varies with the way it is prepared.  However, if you only are interested in ppm of Si and K, you don't need to know n and x because the bag tells you mass % of K2O and SiO2.

Using 27% as a value for the % by mass for K2O, you do the following calculation:

27 g K2O/100 g mix = 0.27 g K2O/g mix = 270 mg K2O/g mix

If you put 1 g mix in 1 liter of water, you have 270 mg K2O/liter and this is equivalent to 270 ppm K2O

In K2O, K is 83% by mass so ppm of K in the solution is 270 ppm x 0.83 = 224 ppm K

In summary, if you dissolve 1 gram of mix in 1 liter of water, you should have approximately 224 ppm potassium.

Of course, you can scale this up or dilute it or concentrate it to get the ppm you want.  You can calculate ppm Si in a similar manner.  If you need assistance doing that, let me know.