TW EASTERN CHEM SINGAPORE PTE.LTD
Application Methods and Attentions of Polyacrylamide
Before the
formal use of a certain type of polyacrylamide product, small-scale tests
should be carried out to determine the optimum dosage and use conditions. When
used as flocculant, the general dosage is about 0.1-0.5 ppm.
Polyacrylamide must be dissolved into a
solution before use, so that the polymer chain can be fully stretched and
reserved. Normally, non-ionic and cationic products are diluted to about 0.1%,
and the dissolution is carried out in stirred tanks of plastics, ceramics or
stainless steel. Since the PAM molecular chain is an
irregular coil in solution, it is easy to intertwine and cross-link between the
coils in preparation and dissolution, so that it has a certain viscosity from
the appearance. A part of
the macromolecule coil structure is deformed and separated from the middle when
using a centrifugal pump with high speed of the impeller rotates. So
that the cross-linking between the
coils is destroyed and the viscosity decreases, which will reduce the use
effect.
The shear force acting on PAM molecular
chains in solution will lead to the breakage and degradation of molecular
chains, which will affect the performance. Therefore, when dissolving and
diluting PAM, the stirring time should be reduced as much as possible, and the
stirring speed should generally be controlled at 50-250 rpm, not too fast. When
using PAM solution, the dosing point should avoid strong mechanical stirring as
far as possible; when transporting PAM solution, the pipeline should be thick
and the number of head changers and branch pipes should be less. It is better
to choose Mono pump or diaphragm pump for transporting pump rather than
centrifugal pump.
Particular attention should be paid to
the operation procedures of dry powder PAM products during dissolution to prevent
the particles from adhering to each other and causing the dissolution operation
to fail. Methanol can be used in small scale test. It can be wetted by ethanol
and other organic reagents to
improve the dispersibility of
particles in water. In
industrial application, it should be added to the container for 1-2 hours
before using, which can be completely dissolved. Instant products can be
dissolved in 0.5-1 hour. Proper heating can accelerate the dissolution of
products, but should not exceed 60 C.
When inorganic flocculant is mixed with
PAM, inorganic flocculant and PAM should be dissolved in two mixing equipments
respectively, otherwise the interaction between the two flocculants will result
in agglomeration and affect the effect. When using, attention should be paid to
the order of feeding. Generally speaking, when dealing with fine particles with
particle size below 50um, inorganic flocculant should be added first. After
that, PAM solution was added. And when the diameter of coarse particles was
above 50um, PAM solution was added to bridge the adsorption process, then
flocculant was added. Users should first carry out small-scale tests to
determine the order of adding.
As a general rule, the more conducive the
solution is to the stretching of polymer molecular chains, the better the
effect will be. Therefore, cationic PAM is suitable for acidic media, anionic
PAM is suitable for alkaline media, and non-ionic PAM is suitable for acidic or
weak alkaline media. Where conditions permit, PAM solution is diluted to
0.01%-0.05% before use, which is conducive to the further extension of
molecular chains, thereby improving the use effect and saving the amount of
use.
PAM products should not be stored in iron
containers. Dry powder PAM can generally keep stable performance for a long
time. The performance of PAM dissolved in water will decrease with the increase
of time, and the lower the concentration, the faster the performance decline.
0.05%-0.1% non-ionic or anionic PAM solution can only be stored for about half
a month. 0.1% cationic PAM solution is extremely unstable. After 1-2 days, the
performance begins to decline. Therefore, PAM products should be ready-to-use.
Because of the uneven arrangement of
lattice ions on the surface of mineral particles and the generation of excess
charges, there is strong influence on PAM effectiveness. The bridging effect of PAM is very difficult to play. It can
only interact with a single particle and suspend in the slurry. If the excess
charges are eliminated by properly adjusting the PH value of the slurry, the
flocculation effect can be increased.
The consumption of PAM is proportional to
the surface area of solid particles. If the diameter of minerals and invisible
sediments is very small, there will be a large surface area and a large number
of PAM will be needed.
If the settling particles are viscous,
loose and charged, it will be difficult to distribute PAM evenly, which reduces
the settling and flocculation effect.
Toxicity
of polyacrylamide:
PAM is not toxic, only when the dosage is
more than 5000 ppm, the absorption of nutrients into the intestinal and gastric
mucosa of animals is obstructed and harmful.
Residual monomers of acrylamide (Am) in
PAM are toxic. For oilfield use and municipal sewage treatment products,
residual monomers are generally allowed to be about 1%. For food use, such as
clarifying sucrose juice for drinking, making paper that may contact food,
etc., the content of residual monomers must be strictly controlled, generally
less than 0.05%.
In 1973, the Japanese Environmental
Health Bureau stipulated that domestic water should not be treated with
macromolecule flocculants. In 1975, the AM content in PAM of sewage treatment
was 0.05%. China stipulates that the amount of
residual monomers of polyacrylamide used in food is less than 0.5%.