Immobilized and Reusable Adsorbent for Removal of Heavy Metals From Water

Abstract

Heavy metals are persistent in many water bodies around us and possess an immediate threat to the health of humans and environment. Majority of the pollutants are impossible to be removed at concentrations below 1 ppm. The current plant adsorbents are immobilized onto sol gel-based product and may be used for an extended period for repeated cycles of adsorptive removal of water. The sol gel-based adsorbent is an inert low-cost immobilized adsorbent that is small in size and can be used for immediate purification of water in containers up to 10 liters of capacity. The physicochemical parameters for the synthesis of the low cost sol gel based adsorbent and desorption thereafter are crucial in the structure and function of the biosorbent.

Specification

Description:FIELD OF INVENTION
[001] Field of invention falls under chemistry, sub category in water purification.
BACKGROUND AND PRIOR ART
[002] Many adsorption studies have been carried out for the bioremediation of heavy metals from natural resources such as soil and water. Many plant parts in their natural and chemically modified form such as neem, drumstick bark, leaves and seeds, mango leaves and other agricultural byproducts have been found to contain compounds that possess ability to chelate heavy metals and thereby reduce the heavy metal load by adsorptive removal. However, the presence of adsorbent residues in water leads to increase in biological oxygen demand and the reusability of the plant-based adsorbents may require desorption and drying for the recovery and reusability of the biosorbent. The time required for the biosorbent to uptake the metals from aqueous media needs to be drastically optimized for rapid treatment of heavy metal pollution in drinking water. The entrapment of biosorbent in a sol gel offers and excellent means for the recovery and reuse of heavy metals from solutions. Our aim is to develop an ecofriendly, low cost and reusable entrapped biosorbent for the uptake of pollutant anions and cations from bench scale volume of water.
SUMMARY OF THE INVENTION
[003] Biosorbents have been used for bioremediation of heavy metal cations from water in batch and continuous modes. The use of these biosorbents is ecofriendly, nontoxic and possesses the ability to chelate metal ions even at low concentrations of less than 1 mg/L of solution concentration. Heavy metals are elemental pollutants that are hard to be removed at very low concentrations and yet possess the ability to accumulate in living systems upon exposure. The current invention uses the immense biosorptive potency of Moringa oleifera leaves that are chemically modified and immobilized in a sol-gel and reused for batch processes upto 10 liters. The biosorbent developed is of low cost and has a longer shelf life to be used in small volumes of water of upto 10 liters and has a long shelf life and reusability for repeated uptake of several heavy metal ions from water. The sol-gel is a microporous, opaque, water repellent and light weight aerogel that does not disintegrate in water and chelated heavy metals from water in a short duration of time. The solgel is easy to use, store and nontoxic and may be used at room temperature for bioremediation of heavy metal ions from water.
BRIEF DESCRIPTIONS OF DRAWINGS:
[004] Figure 1: The sol-gel based biosorbent is shown in the form of a cuboid which can be used to immobilize dried plant based biosorbent (2) for the treatment of heavy metal polluted water as shown in the figure 1. The sol-gel based biosorbent has a porous structure and allows the diffusion of the metal ions onto the surface of the immobilized plant bisorbent. The batch adsorption can be carried out for repeated cycles after desorption of the metal ions from the solution.
[005] Figure 2: Mould containing Monomer solution of Tetra Ethyl Ortho Silicate in solvent phase as Water, Ethanol and Ammonium Fluoride. Addition of Liquor (2) Ammonia as catalyst at pH 2 causes polymerization and gelation of the product (3). Upon drying the biosorbent gets immobilized onto the solgel matrix upon hardening or drying at 50°C which can be used as a solgel adsorbent. The water loaded with heavy metal ions is incubated with the sol gel adsorbent for uptake of metal ions and purify water to improve its potability. The sorbent can be reused for further water purification in a batch like process.
DETAILED DESCRIPTION OF THE INVENTION
[006] The sol-gel based biosorbent is prepared using components such as Tetraethyl ortho silicate, liquor ammonia, ammonium fluoride and ethanol. Tetraethyl orthosilicate, water, ethanol and ammonium fluoride are taken in a volume proportion of 1:2:3.9: 2 along with dropwise addition of few drops of liquor ammonia to facilitate the solidification of the gel at a pH of 2 which was adjusted using 0.1N HCl and incubation at 50°C for 10-14 hours results in transparent, water-repellent, ultralight aerogel . The incorporation of chemically modified Moringa oleifera leaves in the aquous phase (50 mg/ml) leads to dispersion of the biosorbent in the sol-gel and it can be moulded into cubical or cylindrical shape before introduction of liquor ammonia for initiation of the gelation process. The hardened biosorbent after biosorption can be stored at room temperature and repeatedly reused for biosorption of heavy metals from water. It can be used for biosorption up to 10 liters of volume and may be used for repeated adsorption cycles up to 10 times. , C , Claims:[007] 1. Development of sol-gel product requires the mixing of Tetraethyl orthosilicate, water, ethanol and ammonium fluoride taken in a volume proportion of 1:2:3.9:2 and adjusting the pH to less than 2 using 0.1N HCl and gelation is initiated by dropwise addition of liquor ammonia inside the required mould. This invention claims the use of sol-gel with biosorbent dispersed in aqueous phase for uptake of metal ions.
[008] 2. The sol-gel obtained in claim 1 is to be incubated for 10-14 hours at 50°C and hardened for use as immobilized biosorbent for uptake of heavy metal cations from water. The size of upto 10 grams of the sol-gel can be used to uptake upto 20 mg of cations from water in one cycle of batch adsorption for treatment of water.
[009] 3. Chemically modified Moringa oliefera leaf powder is incorporated into the sol-gel for the biosorptive uptake of heavy metal cations. The leaves are treated at a ratio of 1gm of dried leaf powder to 20 ml of 0.1N Citric Acid for one hour and then washed to remove excess acid.
[010] 4. The chemically modified bisorbent in Claim 3 is added to the distilled water in Claim 1 and subjected to gelation upon uniform distribution. This is done to immobilize the biosorbent. The biosorbent may be reused up to 10 cycles of 10L batches of water for the removal of heavy metal cations from solutions.
[011] 5. The immobilized sol-gel is to be stored at room temperature for reusability in air tight containers and has a shelflife of 60days. The sol-gel is moulded into cuboidal or cylindrical blocks of 10 grams of weight or can be reduced in size and used for bioremediation of heavy metal polluted water upon biosorption of metals for a duration of 15 minutes.
[012] 6. The desorption of metal ions can be done by incubating in a solution of 100ml of 0.1N HCl for an hour and the sol-gel can be wiped dry and stored for further usage at room temperature.
[013] 7. The sol-gel based biosorbent mentioned in Claim 4 may be used for uptake of metal ions of up to 20 mg per 10 gram of biosorbent per batch of biosorption at room temperature.

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