Ferric Aluminium Sulfate Alum

ALUM (Ferric and Non-Ferric) Manufacturing Process :

Alum (Aluminium Sulphate) is manufactured by the reaction of Alumina Hydrate and Bauxite with Sulphuric acid.

Bauxite is ground in the pulveriser to 90% passing through 200 mesh and elevated to Batch Hopper through Bucket Elevator. Measured quantity of water is to be taken into the Lead bonded reactor and slowly concentrated Sulphuric acid is to be added in the reactor. After getting the required temperature in the reactor, slowly the ground bauxite is added . After the addition of measured quantity of Bauxite/Alumina Hydrate, the Agitator is kept on for about 45 minutes then the solution is dumped into the settling tank.

The decanted solution of Aluminium Sulphate for the mixed process is then again taken to the Reactor and the required quantity of Sulphuric Acid is slowly added and after getting the temperature. The required quantity (as per the degree of solution) of Hydrated Alumina is slowly added keeping agitator rotating. After the addition of total quantity the Alum is moulded in the trays with the help of tray filling arrangement. The slabs after cooling are to be taken out from the trays and stacked in the store.

The decanted solution for hot process is taken into the evaporator and the solution is concentrated to the required gravity and than moulded in the trays for cooling.

What is Alum and how does it control Algae?

ALUM (aluminum sulfate) is a nontoxic material commonly used in water treatment plants to clarify drinking water. In lakes alum is used to control algae, not by killing the algal organisms, but by reducing the amount of the nutrient phosphorus in the water. Like most other plants, algae requires phosphorus to live an reproduce. Algal growth is usually limited by the amount of that mineral available in the water.

Phosphorus enters the water either externally, from run-off or ground water, or internally, from the nutrient rich sediments on the bottom of the lake. Phosphorus is released from the sediments under anoxic conditions that occur when the lake stratifies and oxygen is depleted from the lower layer.

Even when external sources of phosphorus have been curtailed by best management practices, the internal recycling of phosphorus can support explosive algal growth. Alum is used primarily to control this internal loading of phosphorus from the sediments of the lake bottom.

On contact with water, alum forms a fluffy aluminum hydroxide precipitate called floc. Aluminum hydroxide (the principle ingredient in common antacids such as Maalox) reacts with phosphorus to form an aluminum phosphate compound. This compound is insoluble in water under most conditions so the phosphorus in it can no longer be used as food by algae organisms.

As the floc slowly settles, some phosphorus is removed from the water. The floc also tends to collect suspended particles in the water and carry them down to the bottom, leaving the lake noticeably clearer.

On the bottom of the lake the floc forms a layer that acts as a phosphorus barrier by combining with phosphorus as it is released from the sediments. The floc is harmless to water creatures and aquatic plants. (Sorry, alum does not control rooted aquatic weeds.)

A sediment alum treatment can last up to ten years, depending on how much alum is applied, and lake conditions such as sedimentation rate and external phosphorus loading. Best results are obtained when

steps are first taken to control the external sources of phosphorus . Some of these steps are simple, like encouraging the use of phosphorus free fertilizers and detergents or discouraging large flocks of waterfowl. More costly measures may be necessary such as installing a sewer system, building sedimentation impoundments, and diverting agricultural and urban run-off. Alum can also be used to treat water from a nutrient rich inlet before it enters the lake. Any of these best management practices that are in place before the alum treatment will improve its effectiveness and extend its life.

Uses of Alum

Alum has been part of our lives ever since the time of early Egyptians, who used it in dyeing and purification. Today, it is one of the most widely used and versatile industrial chemicals.

Most of the alum produced today is used in the pulp & paper industry as well as water and wastewater treatment. It is inexpensive and effective for a broad range of treatment problems because it can function as a coagulant, flocculant, recipitant and emulsion breaker. As a coagulant and flocculant, alum removes turbidity, suspended solids and colloidal color, reduces biochemical oxygen demand (BOD) and clarifies potable, process and wastewater.

The main uses of alum are:  

Water treatment: used as a coagulant to remove suspended solids and or some metals (eg Cr, Ba, Cu) from water (either drinking water or in waste treatment facilities) Paper sizing: used as a rosin sizing control in paper production, affects the drainage of liquor from the paper

Other Major Uses

In addition to the primary uses in the pulp & papermaking industry and for water and wastewater treatment, alum is also used in: Cellulosic insulation

Additive to cellulosic insulation

Clay manufacturers

China clay beneficiation

Dyes

Mordant for dyes

Grease manufacturers

Manufacture of aluminum soaps and greases

Industrial wastewater treatment

Sewage and industrial wastewater treatment, emulsion breaking

Manufacture of alumina trihydrate and printing inks

Manufacture of alumina trihydrate for lakes and color extenders

Municipal wastewater treatment

Clarification and phosphorus removal

Potable and process water treatment

Color and turbidity removal

Pulp and paper mills

Process water and mill effluent treatment.

Paper sizing

Soap manufacturers

Manufacture of glycerin from soap lyes

Swimming pools, oil well operators, manufacturers

Water treatment

Tanneries

Tanning furs and white leathers

Zeolite and catalyst manufacturers

Manufacture of zeolites and aluminosilicate catalysts and carriers

What happens at a water treatment plant

For thousands of years people have treated their drinking water to make it look cleaner and taste better. Medical lore from ancient India to Egypt advised that water should be filtered through sand and coarse gravel. In Greece, Hippocrates, the Father of Medicine, recommended boiling water and straining it through a cloth to remove particles.

Early in the 1800s, scientists began to suspect that diseases could be transmitted by drinking water.

Since the discovery of bacteria in the 1870s, treatment to eliminate disease-causing microorganisms has dramatically reduced the incidence of diseases transmitted through water.

Water treatment facilities process water through many steps before it reaches your tap as drinking water for your family. The overall process generally begins with intake at the source, followed by pretreatment, mixing, coagulation and flocculation, sedimentation, filtration, disinfection, and distribution to the tap. See Figure 1. Other steps may be necessary depending on the quality of the water supply.

Preliminary Treatment Processes Preliminary treatment processes to purify water depend on the nature of the water supply and the type and the amount of contaminants. Quality may vary seasonally, thus requiring more or less treatment during certain water-flow conditions. Most groundwater in Alabama receives only the disinfection treatment process. All surface water and water from wells susceptible to contamination from surface water receive full treatment through a filter plant. The various preliminary treatment processes may include the following.

Screening. Large objects such as logs, sticks, fish, and plants are usually screened out at the intake or as the water is drawn into the treatment plant from a river, lake, or other surface water source. If the source is groundwater, the screening is done by nature as the water travels under the surface of the earth.

Pre-sedimentation. Gravel, sand, some silt, and other gritty materials may be removed by fine screening.

Micro-straining. In some cases, algae, aquatic plants, and other very small debris may be removed by still finer screening.

Chemical Pretreatment. The water is conditioned for removal of natural organics, primarily algae and other aquatic microorganisms, as well as their by- products. This may precede micro-straining.

Main Treatment Processes Chemical Feed And Rapid Mix. Chlorine and other chemicals, such as alum or lime, are added to the water to help remove impurities, destroy any taste or odor, raise pH, disinfect, and sometimes remove excess minerals such as iron that may cause rust or staining problems. The water is then mixed rapidly to distribute the chemicals evenly.

Since the early 1900s, chlorine (as a solid, liquid, or gas) has been the primary disinfectant used in the United States because it is effective and inexpensive and can provide a disinfectant residual in the distribution system. Ozone and ultraviolet radiation can also be used as primary disinfectants, but chlorine or an appropriate substitute must also be used as a secondary disinfectant after the main treatment processes to prevent re-growth of microorganisms in the distribution system.

Chemicals may be added to oxidize ferrous iron (Fe++), which is relatively high in some groundwater, to the ferric state (Fe+++). If pH of the water is above 7 (either naturally or by adding lime), the insoluble compound of ferric hydroxide is precipitated.

Softening. Sometimes chemicals are included to reduce the “hardness� or mineral content of drinking water. This usually involves the exchange of sodium for calcium and magnesium and, sometimes, the removal of iron and manganese. However, softening is not as popular as it once was for several reasons. The increased sodium in softened water is unhealthy for people with high blood pressure. In soft water lead is more easily leached from plumbing. Finally, detergents that clean favorably in hard water are readily available. There are no softening plants in Alabama since total dissolved solids are not excessive.

Coagulation And Flocculation. The water is sent into large basins where the alum clings to other chemicals and impurities in the water (coagulation), causing them to form larger, heavier particles called floc. Gravity causes these larger particles to settle to the bottom.

Sedimentation. The water is allowed to sit undisturbed long enough so that solid particles completely settle to the bottom. This process removes chemical precipitates as well as extremely fine clay and organic particles, including dead microorganisms.

Filtration. After flocs (large, heavy particles) settle to the bottom, the water continues on its trip through filters. Layers of sand, gravel, and sometimes hard coal are used to remove any other impurities that are left in the water. Filtration helps to control biological contamination and turbidity.

(Turbidity is a measure of the cloudiness of water caused by the presence of suspended matter.)

Turbidity can shelter harmful microorganisms and reduce the effectiveness of disinfection. Removing organics prior to final chlorination of drinking water supplies is important.

Disinfection. After most impurities have been removed from the water, a small amount of chlorine is added to keep the water from developing bacteria as it travels throughout the distribution pipes. The amount of chlorine (usually no more than 3 parts per million) is carefully measured to be the lowest possible amount needed to keep the water free of germs. Residual chlorine at the tap should be near 0.5 parts per million.

A primary health concern with cholorination is the formation of disinfection by-products. When chlorine combines with organic matter in water, such as decaying plants or animals, it forms substances called trihalomethanes (THMs). These have been shown to cause cancer in laboratory animals. Chloroform is a common THM which has been linked to bladder cancer in those who drink from treated public water supplies. There is a drinking water standard for total trihalomethanes (TTHMs) of 0.10 milligrams per liter, but it applies only to those systems that serve more than 10,000 people.

Fluoridation. In some places fluoride at concentrations up to 1 part per million is also added to help prevent tooth decay. This is not as common as it once was because of the health concern for excess fluoride. EPA has established a maximum contaminant level (MCL) of 4 milligrams per liter (4 parts per million) for fluoride in drinking water.

If conventional steps in the main treatment process are not adequate, certain inorganic and organic

contaminants must be removed by other methods.

Treatment To Remove Inorganic Contaminants Reverse osmosis or ion exchange are used to remove nonmetal inorganic contaminants. Nitrate and fluoride are the nonmetals of greatest health concern in drinking water. Nitrate is frequently found in ground- water supplies in high-density agricultural areas.

Likely sources of groundwater nitrate are nitrogen fertilizers as well as decomposing plant and animal wastes, including human waste from septic systems.

Coagulation and filtration, reverse osmosis, ion exchange, or activated alumina are used to remove metal inorganic contaminants. The metals of greatest health concern in drinking water include mercury, cadmium, selenium, lead, arsenic, chromium, and barium. Industrial sources can contribute rare metals and toxic heavy metals to surface waters.

Controlling corrosion of inorganic chemicals from the distribution or plumbing system is another treatment alternative. Corrosion of plumbing by-products such as copper and lead at the point of use (the consumer’s tap) can usually be indirectly eliminated by controlling pH and water hardness.

Lead contamination is the most serious threat from corrosion. Lead usually enters the water from private plumbing where it is found in solder used to connect copper pipes. Lead can also be corroded from public distribution system pipes and joints.

Aeration effectively strips radon gas from source waters. Oxidation and aeration will remove hydrogen sulfide gas.

Treatment To Remove Organic Contaminants Methods to remove organic contaminants include activated carbon filtration and aeration. Special filters may be used at water treatment plants to remove many toxic organic substances such as pesticides and solvents; however, these filter systems are expensive to build and maintain, and they slow down the treatment process. As water passes through carbon filters, organic impurities are trapped inside the filter material. This is called adsorption.

Sources of organic compounds include storm-water runoff and leaching from improperly disposed wastes, accidental spills, leaking fuel storage tanks and pipelines, pesticides from agricultural areas, and industrial effluents.

Testing - Water samples are taken regularly at many points in the treatment process for laboratory testing. These tests let water plant personnel know whether the primary and secondary drinking water standards set by the EPA are being met. The laboratory equipment being used is so sensitive that it can measure sub- stances in parts per million, parts per billion, or even parts per trillion in some cases.

Chemical Composition of Ferric Alum :

Requirement

Characteristic

1. Insoluble matter % by mass, Max 2. Soluble Iron compound, % by mass, Max *

Grade 1

Grade 2

Grade 3

0.5

0.5

0.25

0.7

0.7

0.35

3. Water soluble aluminium compound as Al2O3 percentage by mass, min 4. pH of 5% aqueous solution, min 5. Basicity (as Al2O3), % by mass, Max ** 6. Additional requirements for material required for purification of water 7. Lead (as Pb) parts per million, max 8. Arsenic (as As2O3) parts per million

16.0

15.0

7.5

2.7

2.7

2.7

0.5

0.5

0.25

30

30

15

6

6

3

* soluble iron compounds (as Fe) , percent be mass , Max permissible for water purification purposes only shall be 1.0 for Grades 1 and 2 and 0.5 for Grade 3 ** the material of Grade 2 can also be supplied as having free acidity (as H 2SO4) of 0.5% by mass, Max, if required by the purchaser, the pH in this case shall not be less than 2.3 Chemical composition of Non-Ferric Alum :

Requirement

Characteristic

1. Insoluble matter % by mass, Max 2. pH (of 5% Solution), min 3. Heavy metals (as pb), parts per million, max 4. Iron (as Fe), percent by mass, max 5. Chlorides 6. Arsenic (as As2O3) parts per million 7. Ammonium Salts (as NH3), percent by mass, max 8. Aluminium (as Al2O3), percent by mass 9. Sodium (as Na) percent by mass, max 10. Potassium (as K) percent by mass, max

Technical Grade

Pure Grade

AR Grade

0.30

0.02

0.005

2.8

2.9

2.2

-

4

10

0.01

0.004

0.002

-

-

to pass test

-

8

5

-

0.025

0.025

17 min

16.6 - 17.6

16.6 - 17.6

-

-

0.05

-

-

0.01

Uses : - Technical Grade (TECH) – used as a mordant in the dyeing of textiles and as a loading material for better grades of paper

- Pure Grade B – used in pharmaceutical preparations and where pure grade of the material is required , namely for clarifying oils and fats , preparation of aluminium resonates and other pure aluminium salts - Analytical reagent (AR) – for use as a reagent in chemical analysis