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Chemical Grouting
Mineral Processing
For many years PQ soluble silicates have been used successfully in chemical grouting to provide soil stabilization and water control during excavation and tunneling. When applied correctly, silicate grouts offer several advantages:
| reliable, proven performance |
| safe application |
| environmental acceptance |
| versatility for a wide range of performance attributes |
There are two ways to set, or harden, liquid sodium
silicates for grouting applications. The first way is by lowering the silicate’s
pH. This causes the SiO2 species to polymerize into a gel. Some setting agents
will hydrolyze over time and form an acid that
will set the silicate. By controlling the composition of the setting agent, and
therefore the rate of hydrolysis, the gel time of the grout can be tightly
controlled.
The second way to set a silicate grout is to react it with soluble metals
to form insoluble metal silicates. These grouts generally have higher strength and
are lower in cost.
Typically, PQ’s N® sodium silicate is used for grouting applications. It is diluted to reduce its
viscosity, so that it penetrates soils more easily. The viscosity adjustment takes into account the soil permeability and the strength requirement of the
grouted mass. The strength of a silicate-grouted soil is influenced by several
factors:
| concentration of silicate in the grout formulation |
| composition and particle size distribution of the soil |
| selection and amount of hardening agents |
| chemistry of the surrounding waters |
Soil grouting and ground modification with sodium silicate is a sophisticated engineering application
and requires specialized equipment and expertise. It is strongly recommended that potential users consult a professional
grouting company with extensive experience in this field before commencing a project. Two such companies are
Hayward Baker(click here) and MULTIURETHANES(click here)
Additional information on soluble silicates grouting applications is available through
PQ's Technical Service Group.
In mineral processing applications, sodium silicate affects the surface chemistries
of particles in ways that enhance the separation of the value (for example,
copper or gold) from the undesirable gangue (for example, clay slimes). Sodium
silicate is used in the ore flotation method of mineral processing. In a
flotation cell, gas bubbles up from the bottom of the cell through a slurry of
raw feed (that is, ground ore). The value particles are attracted to and attach
to the bubbles. They are carried to the surface where they are skimmed off the
top. The gangue particles stay in the water, however, and sink to the bottom,
where they are removed.
The surfaces of the gangue particles must be
hydrophilic (literally, water loving), so that they stay in the water and sink.
The surfaces of the value particles must be hydrophobic (literally, water
fearing), so that they prefer to attach to the gas bubbles and rise to the top.
Various chemicals are added to influence the surface chemistries appropriately.
In some cases, sodium silicate is used as a depressant for such gangue materials
as quartz and silicate minerals. Sodium silicate is also used for some salt-type
minerals, including calcite, fluorite, and barite. The silicate helps to keep
the gangue from floating to the top with the value.
Sodium silicate is
also an important dispersant in flotation operations. For example, silicate
helps to disperse clay particles (just as in detergent applications) that might
be stuck to the gangue or the value, interfering with other chemicals that help
the gangue to sink and the value to rise. The dispersant function of sodium
silicate also improves the efficiency of the pre-flotation grinding step. In
these ways, silicate increases process efficiency and raises both the recovery
rate and the grade of the value.
Details about the effects of
sodium silicate addition on the processing of various minerals and ores are
available through PQ’s Technical Service Group. We can provide guidance and
support for lab and plant trials.
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