Title: Permeable reactive barrier made of steel slag for purifying industrial waste water.
FIELD OF THE INVENTION:
The present invention is directed to a method which utilizes steel slag as a permeable reactive barrier within a flow path of industrial waste water to purify the same.
BACKGROUND OF THE INVENTION:
Steel making slag has several conventional potential applications e.g. usage as a road making ingredient, soil conditioning agent or reflux material in sinter making plant. Unfortunately, all of these were mostly unsuccessful because in all such applications there are some serious shortfalls yet to be overcome. Specifically in road making material application conversion of free lime (CaO) to Ca(OH)2 causes volume expansion of LDS. On the other hand, for soil conditioning application its negative impact due to presence of heavy metal and high Fe content and for reuse as refluxing agent its unacceptably high Phosphorus content are the major drawbacks. Thus an effective utilization avenue of LDS should be explored for generating alternative revenue rendering sustainable valorization.
Considering the foregoing applications, new domain of sustainable application of LDS is being constantly researched to overcome the huge land requirement for storage and natural stabilization. Geotechnical application of LDS as a cost-effective industrial green adsorbent is a completely new idea. The idea has been incubated with comprehensive literature survey known as a Permeable Reactive Barrier (PRB). PRB is a developing technology for in situ ground/industrial waste water remediation which allows selective contaminant to pass through it.

Immobilization of the contaminant may occur through sorption to the barrier materials
or precipitation from the dissolved state. Organic compounds tend to undergo sorption due to
hydrophobic expulsion from the surrounding water. Metals or inorganic compounds, however,
tend to sorb through electrostatic attraction or surface complex ion reactions. Transformation
involves taking the contaminant and transforming it to a less harmful or non-toxic form. An
advantage of this process is that it can be used against a gravity flow to avoid the cost of pressure
and electricity
(KR100476115) Lee Jae Young et all described the permeable reactive barriers comprising zero valent iron and steel slag are provided, wherein the zero valent iron efficiently decomposes chlorinated organic compounds and the steel slag eliminates various heavy metal pollutants within landfill leachate.
(KR100414194) Jung et.al described the cartridge-type permeable reactive barriers for remediating contaminated soil/underground water and remediation method using the same are provided, in which each permeable reactive barrier consists of one or more combination of a slag cartridge, a ferrous cartridge, an organo clay cartridge, and a zeolite cartridge and contaminant plume being diffused along with a hydraulic flow of underground water is guided by several guide barriers arranged in parallel so that contaminants contained in underground water are removed by several reaction mechanisms according to a combination of the installed cartridges.
(KR100597886)
Construction of a permeable reactive barrier described here in a two stage structure of a front permeable reactive barrier part and a rear permeable reactive barrier part, a wastewater treatment method using the same permeable reactive barrier, and a pack-shaped permeable reactive barrier which can be replaced easily at a job site when the life of the permeable reactive barrier ends are provided.

(KR20010044785)
A remediation method of contaminated soil is provided to purify contaminant plume bearing heavy metals, nutrients, COD by using reactive media of blast furnace slag or steelmaking slag.
KR100342766
A remediation method of contaminated soil/underground water is provided to alleviate shock-loads charged on a main permeable reactive barrier by using an auxiliary permeable reactive barrier incorporating blast furnace slag and steel manufacturing slag, thereby reusing waste sources and improving efficiency of the main permeable reactive barrier.
(WO200185618)
Disclosed is a method for treating wastewater with powders of slag generated from steel making process. The method comprises the steps of; flocculating organic matters by introducing into wastewater in the wastewater treatment apparatus provided with an electromagnet a steel slag flocculent comprising 3-30 % by weight of finely powdered steel slags or slag balls and 70-97 % by weight of an inorganic flocculent with an amount of 1-10 % by weight,
(US6602421)
A method for purifying contaminated water involves passing contaminated water through a porous bed of steel slag is described here. The steel slag can be used to remove various contaminants or reduce the concentration of such contaminants, such as heavy metals (for example, hexavalent chromium), chlorinated organic compounds, and certain inorganic anions. The method preferably involves placing an underground barrier of a porous bed of steel slag in a flow path of contaminated groundwater then allowing contaminated groundwater to pass through the barrier to purify the contaminated groundwater.

(CN101045957)
The present invention discloses process of producing polyferric silicosulfate (PFSS) as composite water purifying agent with steel slag and water granulated slag, and belongs to the field of chemical technology. The process includes preparing solution for PFSS with waste steel slag and water granulated slag as material, polymerizing the solution in a polymerizing reactor to produce liquid PFSS, and drying to produce powdered amorphous PFSS.
The present invention utilizes waste steel slag and water granulated slag as cheap material for producing water purifying agent, and the production process is simple, low in production cost, and high in product quality.
(CN101239721B)
The present invention provides a method of PFSS water clarified reagent using industry's steel slag and grain slag as main material.
Al, Fe salting liquid is prepared by sulphuric acid resolving steel slag and grain slag, filtrate and filter residue are obtained by filtering; the filtrate is adjusted pH value to remove Al, adding H2O2 to oxidize ferrous iron being ferric can obtains Fe 3+ precursor; the filter residue is alkali resolved by NaOH solution to obtain Na2Si03 precursor; the two precursors are added in H3PO4 as stabilizing agent, PFSS are prepared by polymerization reaction.
The invention realizes resource regeneration of metallurgical slag, the prepared PFSS has lower cost, better water purifying effect, capable of widely use for purifying factory effluent and domestic sewage such as liquid waste and paper making, printing in steel factory.

(EP1294461)
Disclosed is a device and method for clarifying wastewater, in which atomized steel slag balls are packed in a filtration reactor and suspended solids and organic matter contained in the wastewater are electrically attached to the slag balls and removed by passing the wastewater through the filtration reactor.
(CN203402964U)
The utility model provides a sewage treatment system.
The sewage treatment system comprises a water collecting device, a water collecting pipe, a filter soil assembly and water apron cloth, wherein the water collecting device comprises a water covering tank which is provided with a water outlet; the water collecting pipe is provided with a water outlet section which is designed into a groove-shaped structure, and the water collecting pipe is communicated with the water outlet; the filter soil assembly conveys and spreads sewage through infiltration and comprises a water absorption layer and a surface layer, the surface layer is arranged on the upper side of the water absorption layer, the filter soil assembly is arranged on the upper side of the water collecting pipe, the water absorption layer comprises air-permeable soil, and the air-permeable soil comprises volcanic ash and/or steelmaking slag; one end of the water apron cloth is arranged in the water outlet section, and the other end of the water apron is arranged in the filter soil assembly. Through the structural design, on the premise that the sewage is powerless, the sewage can be continuously purified.

Accordingly, there is a need for a permeable reactive barrier using LD slag for the treatment of ground /industrial waste water. This study investigated the feasibility of using steel making slag as new reactive material for industrial waste water treatment in a cost effective way.
OBJECTS OF THE INVENTION
An object of the invention to propose a design of permeable reactive barrier made of LD slag for the purification of contaminated industrial waste water.
Another object of the invention is to propose a permeable reactive barrier made of LD slag without any chemical treatment, which can be placed directly at the flow path of contaminated plant effluent for purification.
A still another object of the invention is to propose a permeable reactive barrier made of LD slag, which act as a barrier for contaminated plume and purify the contaminated water without any extra energy.
A further object of the invention is to propose a permeable reactive barrier made of LD slag, which helps in reduction of the colour present in the plant waste water.
A further object of the invention is to propose a permeable reactive barrier made of LD slag, which helps in reduction of the free lime present in the slag,
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a preamble reactive barrier made of steel slag for the removal of contaminates comprising: of five consecutive chambers. A water inlet system is made in

the 1st chamber which is the reservoir of plant waste water and from this chamber water flows down from first to fifth chamber sequentially.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
FIG 1: shows the permeable Reactive Barrier made with LD slag at Sunsungaria
FIG 2: Shows the variation of free lime with time
FIG 3: Shows variation of pH with time
FIG 4(a) and (b-e): shows % Retention of colour of BOT water with time
DETAILED DESCRIPTION OF THE INVENTION
Present study deals with the development of permeable reactive barrier with LD slag to remediate the contaminated plant effluent. The main advantage of a PRB is that, generally, no pumping or extra treatment is required; the barrier acts passively after installation. Along with the site monitoring depending on the longevity of the reactive medium the barrier may have to be rejuvenated / replaced periodically. The contaminated plant water when passed through this "permeable system" possessing sufficient hydraulic conductivity results in its purification, where reduce the colour of BOT water and free lime of the LD slag to make it usable as road making material.

Methodology: adapted by the inventors The Design Methodology
PRB design involves the following steps:
1. Preliminary assessment
2. Site Selection
3. Reactive media selection
4. Treatability testing
5. Selection of a suitable fabrication method
6. PRB designed
7. Experimentations
8. Economic evaluation.
The preliminary assessment was conducted to evaluate the technical and economic suitability of a given site for PRB application. After site selection PRB was designed with suitable material.
Design of PRB:
In the broadest sense, a PRB is a continuous, in situ permeable treatment zone designed to
intercept and remediate a contaminant plume. The term "barrier" is intended to convey the idea of a barrier to contaminants but not to the water flow.
This PRB structure consists of five consecutive chambers separated by 3.75mm MS plate. A water inlet system was made in the first chamber which was the reservoir of plant waste water. From this first chamber the water flows down to the 2nd chamber through the wire net placed at

the bottom of 1st chamber. 2nd chamber was the first PRB zone, filled with the LD slag of size 20-40mm. The two chambers filled up with nearly 5-6 tons of material. Water exposed to slag was over flowed to the 1st Tank. Next step was the water to flow in the 2nd PRB which slowly accumulated in the 2nd tank. Flow rate adjusted to 434 L/hr. Figure 1 shows the configurations of present PRB systems.
RESULTS AND DISCUSSIONS
Chemical analysis: Chemical analysis was performed at our chemical lab with feed slag, collected from the plant and used slag, collected from our experimental set up after 15 days of exposure.

Volume expansion and stability:
Due to the presence of unstable phases in its mineralogy, steel slags can show volumetric instability caused mainly by the presence of free CaO. The aging of steel making slag is essentially a hydration reaction of CaO. In the presence of water, free lime hydrates to form

hydrated lime or portlandite (Ca(OH)2). Portlandite has a lower density than CaO and hence hydration of free CaO results in volume increase. The hydration mechanism of CaO were studied and proved that when it is immersed in water compacted CaO can hydrate almost completely in a few days with a volume increase as high as 100%.

In this reaction heat is released and the lime expands making the slag volumetrically unstable. To check the expansion stability of the treated slag we have done the volume expansion test of the feed and treated slag with the help of volume expansion equipment This test results shows that the expansion stability ratio fully satisfies the standard value of water-immersion expansion stability ratio (expansion stability ratio) of ≈ 1.5% as specified in JIS A 5015 "Iron and steel slag for road construction, and it could be confirmed that there is no problem as to the expansion stability of the treated slag.
The chemical composition of feed and treated LD slag is represented in Table 2.

In this way slag can be volumetrically stabilized by natural aging without using any chemicals or energy. This slag could be used in road making purpose.

Variation of free lime:
Pilot test results reveals that the treated slag contains less amount of free lime (10.60 ppm) in comparison to the feed slag (12.50 ppm), which because of the hydration reaction of the CaO during our experimentation. This results corroborated by the lab data (Figure 2), where initial free lime content of the slag exposed in waste water was 7.8 ppm which after 15 days came down to 2.5 ppm.
Variation of pH:
The effect of pH on the mobility of organic/ inorganic ions demonstrates that a strategy involving pH control can be an effective contaminated water remediation remedy. It is well known that the dissolution of Ca from slag into waste water results in the increase of the pH value. Actual pH of plant effluent was 8, which suddenly increased up to 12.2 after 24 hours of exposure to slag. This is due to the dissolution of Ca from slag. The slag contains large amount of Ca in the form of Cao, Ca2SiO4 etc. The Ca concentration increased greatly with increasing the exposure time and also the amount of slag in the PRB. Calcium silicates react with the experimental water by the following proposed reactions:


Each of these reactions releases calcium ions and consumes protons, creating a Ca-OH waste water and ultimately the Ca(OH)2. The production of the hydroxyl radical that leads to higher pH conditions results in the precipitation of certain carbonate and other compounds within the slag surface and this can finally lead's to a porosity loss. Also since our experiment was done in the open system the lime reacted with atmospheric CO2 to form insoluble carbonate which was adsorbed by the void part of the slag.

Formation of above mentioned insoluble Ca(OH)2 and CaCO3 helps in gradually neutralising the pH of the waste water as shown in Figure 2.. The concentration of pH is ultimately depends on the quantity of slag and exposure time. The discharge of water with neutral pH (8.0) was thus possible by using the PRB made with LD slag.
4.S Retention of Colour:
The important natural resource i.e water is being contaminated by various industrial activities. The untreated industrial wastewater discharged into the environment causes the contamination of soil, water and air. This ultimately affects the environment adversely. Most of the industrial effluents contain colour as a contaminant. The discharge of untreated wastewater from industries may contribute colour to the receiving water. Hence, it is necessary to treat the industrial effluents to reduce the concentration of colour prior to its release into the environment.

LD slag is considered to be effective in adsorbing phenolic impurities of the waste water because of the presence of calcium di silicate compound. Treatment of waste water with LD slag led to a clear solution. The treated water when characterized using absorbance as a parameter for colour measurement promising results has been obtained. In our experimental work we allowed the BOT water to pass through the PRB made by LD slag. It is seen from the experimental results (Figure 4 a-e) that LD slag is a good colour absorbent. Here within 200 hours nearly 85 % colour removed from the waste water without any chemical dosing or addition of colour removing agent. This was again in the comfortable range to discharge the water in the atmosphere.

WE CLAIM:
1. A preamble reactive barrier made of steel slag for the removal of industrial waste water contaminants comprising of five consecutive chambers. A water inlet system is made in the 1st chamber which is the reservoir of plant waste water and from this chamber water flows down to from first to fifth chamber sequentially.
2. The preamble reactive barrier as claimed in claim 1, wherein 2nd chamber is the 1st PRB zone filled with the LD slag of size 20 to 40mm.
3. The preamble reactive barrier as claimed in claim 1, wherein the first two chambers are filled up with nearly 5 to 6 tons of material.
4. The PRB as claimed in claim 1, wherein each consecutive chamber is separated by 3.75 mm MS plate.
5. The PRB as claimed in claim 1, wherein the said water flow from chamber to chamber is adjusted at a rate of 434L/hour.