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Aluminum_Sulfate
by wacle 2012-01-09 18:04:02
632 Views, 스크랩 스크랩

           Alumimum  Sulfate

Aluminum sulfate –more familiarly, alum- has been known to mankind since the beginning of

recorded  time. As early as 2000 B.C. naturally  occurring alum was in use by the Egyptians as a

mordant to speed dyeing,to fix the dyes and to improve their color…takes which later assumed even

greater importance and which still consume limited quantities of this salt.  Pliny mentions alum

in his comprehensive “Natural History” and its use as  an agent for the softening of hides was

recorded during the early years  of the Christian era. For even longer man has known aluminum

sulfate improves  the durability of parchment and its receptivity to pen and ink. Modern paper

makes add it during processing for similar purposes, an important, that it requires two-thirds of all

alum produced.

 

In this country, aluminum sulfate was among the first of the heavy chemicals to be produced… With

records showing the colonists using domestic material  as early as 1635. Exactly two hundred and fifty

years later, Stauffer  Chemical Company was established to supply chemicals for industry and  

agriculture, and the company has been for many years a primary source for  aluminum sulfate.

 

Alum no longer is a product of varying composition derived by crude production methods.

In modern chemical plants, it is manufactured under  carefully controlled conditions and carefully

assayed. Commercial alum is available in two physical forms; as a dry material ground from partially

dehydrated slabs and in aqueous solution commonly known as “alum liquor”.

 

Chemically speaking, “alum” denotes the hydrated double sulfates of aluminum with univalent metals

or radicals such as potassium, sodium or ammonium.  It is erroneous to speak of aluminum

sulfate as “alum” but it is the nature of people  to shorten long words or terms in frequent use,

so that “alum” for “aluminum sulfate” prevails among speakers in industrial and water purification

activities.  It refers both to the single salt, also known as commercial alum, paper makes’ alum or filter

alum or to the double salts known as crystal alum, ammonium alum, potassium alum or sodium alum.

 

Water treatment: Surely, one of the most important processes in our complex economy is the

maintenance of a pure water supply. So it is the  second largest consumer of aluminum sulfate is

the water treating industry.

 

For human consumption, water should be clear, colorless, odorless, tasteless  and free from harmful

bacteria and chemicals.

 

For Industrial consumption, the quality requirements vary greatly, due to the  varying requirements

of industry.

 

Water to meet municipal and industrial requirements must be produced from a variety of sources

ranging from wells to different sources of surface waters requiring a corresponding variety of

treatment.

 

The most important chemical used in water treating is aluminum sulfate as a coagulant.

Coagulation is employed to remove the turbidity caused by suspended and colloidal matter. It also helps

to remove bacteria and control taste and color. With lime and  soda ash, aluminum sulfate is used for

water softening.

 

Alum, when added to the inflowing water supply reacts with the alkalinity naturally present, or the

alkaline materials added to adjust pH, to form gelatinous flocs of aluminum hydroxide which absorb

and entangle the colloidal impurities present and cause them to settle out.  Equation 1 below

illustrates the reaction of alum with the natural alkalinity of calcium bicarbonate; the second equation

shows the reaction with lime and the third equation shows the reaction with soda ash. In each case

A1(OH)3

1.     AI2(SO4)3

2.     AI2

3.     AI2

Experience has shown that the reduction in alkalinity which takes place where alum is added is far less

than that called for by any of the above reactions. Thus there are other distinct reactions which product

coagulation:

 

1.     The trivalent positive aluminum ion, when added to negative particles of color or turbidity,

exerts its great coagulating power, neutralizes and charges particles of color or turbidity,

and coagulation begins.

2.     The tiny particles first agglomerated, micro-flocs, may still possess positive charge and can

therefore continue to neutralize negatively charged particles which settle rapidly to produce

clean, sparkling water.

3.     As it grow, the gelatinous floc tends to occlude or envelop; some adsorption may take place.

This results in suspended turbidity forming larger particles which settle rapidly to produce

clean, sparkling water.

 

In any water supply many factors influence the conditions which are needed to produce a good floc

which will ensure cleat, sparkling water: Among these are:

  1. The nature and concentration of color turbidity and other impurities (such as organic

compounds, bacteria, algae) in the raw water.

  1. Alum dosage-which is usually predetermined by the jar test influences both the amount of

floc and ate of flocculation.

  1. The pH. Every raw water has its own optimum pH at which the floc Performs most efficiently.

The effective range for alum is 5.0 to 9.0 It is often necessary to adjust the pH of raw

water with alkali to the effective range.

  1. The temperature. The rate of floc formation varies directly withthe temperature. Lower

temperature means slower floc formation which is sometimes hastended by increased

dosage of alum.

 

In practies, alum is usually fed to the raw water from a dry feed machines at an optimum rate

(dosage) predetermined by a jar test. If alum liquor is used instead of the dry material, the feed is

governed by a calibrated flow meter. Stauffer’s alum liquor is supplied at constant strength to

in sure the operate of correct dosage. After flash mixers distribute the alum uniformly through

the water, the water is slowly agitated in the flocculators. The small particles now coalesce

as settleable “floc”. After the floc has settles, the clarified water is usually passed through sand

filters to remove any remaining suspended matter.

 

Sewage treatment: Alum is also used by some municipalities for the sewage. Its purpose is twofold:

1.     As in water purification, to coagulate the suspended any colloidal particles of the sewage.

2.     For conditioning of sewage sludge on sludge-drying beds.

 

When alum is added to raw sewage, it forms a floc which envelops and adsorbs both the

suspended particles and colloidal matter. Coagulation is faster than in the purification of water

because the concentration of solids is higher is sewage.

 

As in water purification, the sewage treating equipment consists of a preliminary settling basin,

a flash mixer, coagulation tank and sedimentation basin. The process is much the same.

After preliminary settling, the flash mixer mixes the dosage of alum uniformly. This coalesces

the floc and suspended matter, which is removed in the sedimentation basin. When

used properly, alum reduces efficiently both the suspended solids and Biological Oxygen

Demand (B.O.D) within a pH range of 5.5 to 9.0. Actual dosage of alum is determined by

experience or preliminary jar test.

 

The presence of alum in the settling sludge will not affect further digestion and makes the

dewatering problem easier. The settled digested sludge is usually driend in sludge beds.

Alum at this point is used as a conditioner which will produce a good semi-dry cake for easy

removal and further drying in a kiln. The dry sludge from the kiln is used as the organic

nitrogen component in mixed fertilizers.

 

Water flooding: In petroleum production water may be injected into subsurface strata for either

of tow major purposes:

1.     To simulate production: (In some cases the additional production stimulated by water

flooding exceeds the primary recovery from the reservoir)

2.     To dispose of the residual water produced with the oil to prevent Contamination of fresh

water sources.

 

   In both situations the water must be treated before injection into the well. To remove organic and

other suspended matter, sedimentation with alum is customary. Alum is used here in conventional

water treatment for flocculation or coagulation.

   Fire Fighting: Most large petroleum refineries and/or outlying tank farms employ  a two-solution

wet-foam system for smothering tank fires. Foam solutions of aluminum sulfate and bicarbonate of

soda are stored in separate tanks in these areas in case of fire in an oil tank.

 

The tanks are equipped with foam-mixing chambers, located at the top ring or roof of the tank,

which combine the two solutions to make a chemical foam. The foam, spreading on the surface

of the burning oil, starves the fire by removing the oxygen.

 

 Synthetic Rubber: In the rubber industry, alum is used for the conditioning of process water and

as a coagulant in the manufacture of synthetic rubber of the butadiene-styrene copolymer type,

known as SBR. In making SBR, the butadiene and styrene are fed separately into a reactor with

water and a catalyst, all subjected to agitation at controlled temperature. When most of the material

is reacted, the process is stopped to forestall diminishing efficiency, the unreacted material stripped

off and returned to raw stock.

The remainder, which is almost identical with latex from a rubbertree, must be coagulated and

aluminum sulfate is one of the agents used for this purpose. The coagulated rubber polymer,

know as “crumb”, is drained, filtered, washed, dried in hot-air dryers and pressed into bales

ready for processing to finished products.

 

Waste Disposal: Increasing regulation by state and local agencies is forcing many manufacturing

plants to treat waste effluents previous to discharge into streams or sewers. Alum is used to

coagulate and solids in these wastes.

 

Grease and Oil Recovery: By the use of aluminum sulfate in pneumatic type waste

disposal plants, valuable oils and greases are reclaimed. KA type of reverse settling and

coagulation is used whereby the flocs of alum and entrained or trapped oil are floated to the

surface by air- bubbling and are removed by skimmers.

 

Other Uses of Aluminum Sulfate is a raw material for the manufacture of the  double salts-

the true alums- and other aluminum salts and as astringent in deodorants. It is used in the

purification of by- product glycerin and as a fire-retarding agent for insulating materials.

 

Iron-free aluminum sulfate is used as a dye reagent in making greenish blue lakes; as a tanning

reagent in the manufacture of white leather such as that used for baseballs; as a mordant or

color-fixing agent in textile dyeing. Leached with lime, it makes "satin white" a paper coating material.

 
 
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