Evaluation of Alum and Purification Process of Water by Coagulation Method

Introduction

Alum is a mineral substance that is obtained from nature in pure and impure forms. It is obtained from aluminum ore (mineral salt). It can be clear, colorless, odorless, and crystalline and tastes like a sweet astringent. It has a molecular weight of 458.28 gm [1]. It is found in many pharmaceutical, cosmetic, and food products. It has a strong astringent quality. It comes in four different colors: white, green, yellow, and red. White is known as phitkari, green is known as heera kasees, yellow is known as kasees, and red is known as surkh phitkari [2]. When heated, it melts and loses its water of crystallization at around 200 degrees resulting in an anhydrous salt. It is frequently contaminated with impurities in markets. It can be made suitable for therapeutic use by dissolving alum in boiling water and the solution is filtered and evaporated to produce crystals which should be stored properly for future use [3].

Alum is a chemical that is used in dyeing textiles by Egyptians in ancient times. Historic people believed that Egyptians hardened the papyruses with alum. Pliny (roman historian) stated that alum acts in both the cosmetic and medical fields. Many people believed that alum was only used as a deodorant. In the 12^th century, alum was still a common chemical that is used in the medical field as well as in dyeing textiles. It is commonly found in dry and desert regions. Alum was imported from North Africa or in surrounding regions. In the 17^th century, the alum extraction method was developed by British people. In the 19^th century, British people used alum in a bakery for making bread due to its better appearance. From the 20^th century, baking soda was a competitor for alum but alum won [4].

Properties of alum [3]

Organoleptic character- White and transparent crystalline in nature.

Solubility- Highly soluble in water (especially in hot water).

Boiling point- Around 200 ⸰ C

Melting point- 92.5

Density- 1.725 g/cm 3

Application of heat- Alum crystals are liquefied if heat is applied

Action on litmus paper- Blue turns to Red

Types of alum

Potash Alum is commonly named potassium alum. The chemical formula is KAl (SO₄) ₂·12H₂O and potassium aluminum sulfate is its chemical name. The molar mass is 258.192 g/mol. It is white crystalline in nature and smells like metallic water. Potash alum is also sometimes called white alum. Soda Alum is also called sodium alum or just SAS. Sodium aluminum sulfate is its chemical name and has a molar mass of 458.28 g/mol. It can be in white crystal or powder form and has a smell of metallic water. The chemical formula is NaAl(SO₄)₂·12H₂O. Ammonium Alum is referred to as ammonium sulfate alum. The chemical formula is NH₃Al (SO₄)₂ ·12H₂O. Molar mass of 132.14 g/mol. It exists in a small white crystalline form with a metallic water smell. The common abbreviation of Chrome Alum is CAS. It is commonly called chromium alum and has a chemical formula KCr(SO₄)₂·12H₂O. It is also known as chromium potassium sulfate and has a molar mass of 283.22 g/mol. Like other alums, it has a metallic water smell but mostly exists in a purple crystal form. Selenate Alum is commonly known as aluminum selenate. In this form of alum, selenite is present instead of sulfate. It acts as a strong oxidizing agent. The molecular formula is Al₂O₁₂Se₃ and its molar mass is 482.9 g/mol [5].

Uses of alum

Potash alum is used in baking powder, pickling leather, water clarifier, aftershave, and fireproof clothes. Soda alum is most commonly used in baking soda and the food industry it acts as an acidulant. Ammonium Alum is commonly used in tanning, dyeing in textiles, flame retardant processes for textiles, and in the manufacture of certain types of cement, glues, and deodorants. It may also be used in water purification systems. Chrome alum has a deep violet color, and is commonly added to other types of alum to grow purplish crystals. It is most commonly used in leather tanning. Selenite alum is used in the preparation of antiseptics. Apart from these uses, alum also has therapeutic properties like Anti-microbial, Anti-platelet, Anti-obesity, Anti-haemorrhagic, Anti-inflammatory, Anti-Dandruff, and Anti-asthmatic [6].

Role of alum for water treatment

Alum can be used to treat contaminated water in the water purification processes and to act as a coagulant in the Coagulation-Flocculation processes. It is a chemical Water treatment technique used before the sedimentation and filtration process. It is used to enhance the ability of water purification by removing large sedimented particles. Purification is done by Coagulation and Flocculation. It destabilizes the charge of the particles present in the sample. Coagulants(alum) with opposite charges (positive) of the suspended solids are added to the water to neutralize the negative charges on dispersed solids (clay and organic substances). Once the charge is neutralized, the small suspended particles stick together and micro flocs are formed. Micro flocs are nothing but slightly large particles that formed and they are still too small to be visible to the naked eye. In other words, it is a chemical Water treatment technique done before the sedimentation and filtration process to strengthen the proficiency of the treatment and its ability to remove polluted and dirty particles. Flocculation is the process where a chemical coagulant is added to the water to stimulate bonding between different types of particles. This leads to the creation of larger aggregates that can separate easily [7].

Materials and Methods

Chemicals required Potassium sulfate, Ammonium sulfate, Sodium sulfate, Ammonium sulfate, concentrated sulphuric acid, and Distilled water.

Apparatus required Beaker, China dish, glass rod, tripod stand, and funnel Equipment required Hot plate.

Preparation of potash alum [8]

15 grams of potassium sulfate was weighed and transfered into a beaker. To this, 60ml 0f distilled water was added and stirred continuously. Slightly warm the solution. Keep the solution aside (beaker 1). In beaker 2, 60g of aluminum sulfate and 90 ml of distilled water were taken and 6 ml of concentrated sulphuric acid was added and the solution was stirred continuously to get a clear solution (beaker 2). Both the solutions were mixed and transferred into the china dish after passing them through filter paper. The solution was heated continuously until it reached the crystallization point. To check the crystallization point, take the stirring rod out of the china dish and blow some air on it. The formation of crystalline crust on a glass rod after blowing air is a sign of reaching crystallization.

After this process, the china dish was removed from the burner and kept in an ice bath after covering it with a watch glass overnight. After crystals are formed, crystals are filtered from the mother liquor and dried using filter paper.  The product was weighed and the percentage of yield was calculated and reported.

Preparation of ammonium alum

47.4g of aluminum sulfate was Weighed and transferred into the beaker, and 45 ml of hot water was added to dissolve and make up the volume of 75 ml (beaker1). Weigh 23.1g of ammonium sulfate and transferred it to another beaker, 45ml of distilled water was added to dissolve and make up a volume of 75ml (beaker2). Both solutions were mixed to form ammonium alum. The solution was kept overnight at room temperature to get small crystals. Reheat and cool to obtain large crystals. After 1-hour crystals are formed. The product was weighed and the percentage of yield was calculated and reported.

Preparation of soda alum

31.6g of aluminum sulfate was weighed and transferred into the beaker, 30ml of hot water was added to dissolve and make up to 50ml with distilled water. 13.2g of sodium sulfate was transferred to another beaker, add 30ml distilled water was, and make up the volume. Two solutions were mixed in the china dish and boil the solution on the burner. After boiling, the solution was kept in an ice bath overnight. Crystals are formed, dry, and weigh the product.

Evaluation tests for alum

A. Solubility:

Add 0.5g of solid sample to 1 ml of distilled water in a test tube. Stir gently with a glass rod. Record the observation [9].

B. pH:

Before the determination of pH, the pH meter was calibrated.  1g of prepared alum was dissolved in 100 ml of distilled water in a beaker. pH was measured using the pH meter.

C. Identification test: [10, 11]

1. Flame test (Test for potassium)

The small amount of alum was taken in a spatula and ignited in the direct flame.

Observation: Lavender color flame

Inference: presence of potassium

2. Flame test (Test for sodium): Take a small amount of alum in a spatula and ignite it under a direct flame.

Observation: Yellow color flame

Inference: presence of sodium

3. Test for ammonium: 10 mg of ammonium alum was heated with sodium hydroxide solution; ammonia is evolved, which is recognizable by its odor and by its action on moist red litmus paper, which turns blue.

Observation: Red litmus turns to blue

Inference: Presence of ammonium

4. Test for aluminium:20mg of the potash alum was dissolved in 2 ml of water, 0.5 ml of 2M hydrochloric acid was added and about 0.5 ml of thioacetamide reagent; no precipitate was produced. 2M sodium hydroxide was added dropwise; a gelatinous white precipitate was produced which re-dissolves on the addition of a further 2M sodium hydroxide. Gradually ammonium chloride solution was added.

Observation: A gelatinous white precipitate was obtained

Inference: Presence of aluminum

5. Sulfate test:50mg of soda alum was dissolved in 5 ml of water and 1 ml of dil. hydrochloric acid was added and 1 ml of barium chloride solution.

Observation: A white precipitate was obtained.

Inference: presence of sulfate.

Selection of water sample

The water sample was collected from various part of Chennai and the sample name was given as follows Perambur (WS1), Sriperumbudur (WS2), Retteri (WS3), Ernavoor(WS4) Maduravoyal (WS5).

Semi-quantitative evaluation for water samples

Limit test for chlorides, sulfates, iron, and lead was performed for all different areas of water as mentioned in Indian pharmacopeia [12, 13].

Determination of sodium content by flame photometry method

Preparation of a standard solution

0.548g of sodium chloride (equivalent to 0.23g of sodium) was dissolved in 100 ml of distilled water. 1,2,3,4,5 ml of solutions was pipetted out in five different volumetric flasks and the volumes were made up to 100ml with distilled water to get a solution of 1,2,3,4,5 millimole of sodium or 2.3,4.6,6.9,9.2,11.5 mg of sodium per 100ml respectively [14].

Preparation of sample solution

2ml of water sample was dissolved in 50ml of distilled water. The standard solution was introduced into the flame and emission intensities were measured at 589 nm and the sample solutions were also measured as the same. A calibration graph with a concentration on x- the axis and intensity on y- the axis was drawn [15].

Purification of groundwater by prepared alum

 The method adopted is coagulation. 100ml of groundwater was taken in a beaker 0.1g of different types of alum was added to a beaker containing groundwater. Kept aside overnight. The solution was filtered [16].

IN-VITRO antibacterial activity

Method: Agar well diffusion

Organisms: Gram-negative bacteria: Escherichia coli,Gram-positive bacteria: Staphylococcus aureus

Medium: Mueller Hinton Agar (MHA)

Alum in the form of crystals pounded using mortar and pestle. It was weighed using analytical balance as 0.5g, 1.5g, and 2.5g. It was dissolved in 10ml distilled water. So that the concentration obtained in percent is 5%, 15%, and 25%. The prepared sample solutions were used for antibacterial activity by the Agar well diffusion method [17, 18].

Results and Discussion

Preparation of alum derivatives

1. Potash alum:

• Theoretical yield – 40.83g
• Practical yield- 33.91g
• Percentage yield- 83.00%

2. Ammonium alum:

• Theoretical yield – 79.24g
• Practical yield-94.03g
• Percentage yield-118.66%

3. Soda alum:

• Theoretical yield -42.58g
• Practical yield-45.61g
• Percentage yield- 107.11%

Physical properties

Chemical test

 (+) represent Positive result, (-) represent Negative results

Limit test

The limit test of chloride, sulfate, iron, and lead in different areas of water was performed. The opalescence, turbidity, or color produced before alum treated water sample is more than after alum treated water. Therefore, the alums absorb the ions from groundwater and purify the water.  The results are tabulated (Table 3).

Determination of sodium content by flame photometry

The determination of sodium present in the sample was performed by flame photometry. The test concentration of water samples is compared with standard sodium chloride. The values are tabulated (Tables 4 and 5). From the table, it is observed that all derivatives of alum absorbed the sodium ion from the groundwater samples.

In vitro antimicrobial activity

The in vitro antimicrobial activity for three different alums was performed. The results are tabulated. The zone of inhibition was measured. From Table 6, it was observed that the three different alums were active against both gram-positive and gram-negative bacteria antibacterial activity. Among the three different alums, soda alum produces the highest antibacterial activity against both bacteria.