Silica removal 2

[lattar]

Does anyone have experience of removing silica from water or salt solutions with polyaluminium chloride (PAC) or with other flocculation process like co-precipitation it with magnesium hydroxide?
Thank you for your time, Lattar

 

[arbochim]

if you have silica you can better dissolve them with hf than neutralize hf with calcium hydroxyde to make precipitation

 

[cub3bead]

Silica will be removed from water during lime softening operations. It is more efficient if the water is hot such as in a hot process softener. If you do not have sufficient Mg in the water you can add it by feeding MgCl2 which will preciitate as Mg(OH)2. You will need to operate at a pH above 10.2. MgCl2 is more efficient that feeding Mg(OH)2.

The old Drew water handbook has an excellent discussion about the chemistry.

Arbochim, the problem is reducing silica in a solution not dissolving more into the solution.

 

[DeltaCascade]

Applebaum's good old 1968 or so text, "Demineralization by Ion Exchange" has a good discussion ... for example, MgO to Silica ratios required for specified silica reductions, as well as discussion of other chemical agents for silica removal in warm or hot lime softening. Silica removal with MgO is common, and it is more of a co-adsorption process.

 

[annmariehopkins]

Silica comes in two forms, non reactive (colliodal) and reactive which has a small charge. Most waters contain a mixture of the two forms, usually reactive silica has the higher concentration. Any coagulant, such as PAC, used to form a floc followed by a clarifier or filter will remove much of the non reactive silica.
To remove the reactive silica you need another process such as those described above. Membrane process are also commonly used for silica removal. Which you choose depends on the concentration of silica in the water and what the water is going to be used for.