A Method And A Device For Reclaiming Green Waste Foundry Sand
About the Practice
Foundry industry is one of the largest consumers of sand. The sand is used in foundries for the production of molds and cores. When molten metal is poured into these molds, higher temperature (> 700 °C) leads to the deactivation of binders present in the sand. The transformations and changes that take place in chemical composition, mineralogy, morphology of the foundry green sand are due to the casting process. These properties change due to the presence of dead bentonite. The deactivated binder forms a brittle coating on the surface of sand making it useless for further molding operations. The removal of this dead binder, so that the waste sand can be recycled and used again, is a challenge. The presence of dead binder results in dumping of huge quantities of sand either in a landfill or creation of sand hills. This dumped waste foundry sand contains many heavy metals which can leach inside the ground and cause ground water pollution. Moreover, the open sand hills result in enhanced particulate matter in the surrounding areas causing risk to health and life. Thus, waste foundry sand, if untreated, poses risk to both environment and life. Hence, a need was felt to develop a cost effective, multiscale solution to address the issue and reclaim the waste foundry sand Binder such as bentonite, is used in the preparation of green sand for molding purpose. It is aluminium phyllosilicate consisting mostly of montmorillonite clay mineral. Montmorillonite has an alternating tetrahedral structure of both silicon and aluminium atoms surrounded by oxygen. This results in a layered structure which appears as flat plates. Water is adsorbed on these plates and this is the reason why bentonite expands when mixed with water, and shrinks when dry. The surface of bentonite is ionic which, in the presence of water, helps in creation of sticky coating on the surface of sand grains. This property of bentonite is responsible for the production of moulds. Bentonite has huge water absorbing capacity and a significant potential for cation exchange. The water molecules are trapped in the interstitial sites. At around 100–200 °C, water held between planar sheets is lost while structural water, i.e. the hydroxyl groups start disintegrating at around 450–500 °C. Furthermore, heating to around 850 °C, leads to the breaking of crystal structure and unwanted phases like cordierite, mullite etc. formed. According to a report by Coastal regulation zone notification Ministry of environment and forests (2011), the government of India has banned sand mining in many places which have resulted in a sharp increase in the cost of fresh sand available. The government of Maharashtra also issued a notice to foundries operating in the state in 2014, which prevents them from dumping the waste sand near Industrial area. The nearest dumping site is typically more than 250 km away from the nearest foundry cluster. These medium and small scale foundries cannot bear the dumping costs associated with waste sand. Some large scale solutions are available in the market but none of these are suitable or economical for small and medium scale foundries, which generally require reclamation capacity as low as 1 TPD. These reclamation units are of big capacity like 5 TPH and mostly based on the thermal reclamation (energy intensive). Therefore, small and medium scale foundries cannot afford these units for WFS reclamation. All in all, there is an urgent need for cost effective solution at small or medium scale to address this problem and we believe our innovation would serve the purpose. We have developed a two-stage attrition device which reclaims waste green sand cost-effectively and caters the need of small scale foundries. This device can also be scaled up as per the foundry’s requirement. The device can be installed either inside foundry or can be installed for a cluster (group of small scale foundries). The existing solution can make foundries partially independent on sand mining and improve the economics of the foundry.
Detail:
India is the second largest producer of casting and second largest consumer of sand in the World. Foundries generate Waste Foundry Sand (WFS), contains toxic heavy metals and particulate matter, which makes its dumping an environmental and health hazard. In India, more than 80 % of the foundries are medium and small-scale. These foundries cannot afford costs, associated with dumping and treatment of waste foundry sand. Stringent regulations of Pollution Control Board and the Ministry of Mines regarding waste disposal and sand mining has brought many of these small-scale foundries on the verge of closure. A lot of research has been done to use WFS in other industries like construction and ceramics, but not much has been done to reclaim and use waste sand within the foundry itself. So, there is an urgent need for the development of a reclamation technology that is economical. This would not only suffice the need of the foundries, but also address the environmental issues. The problem with the WFS is dead clay that deposits on the sand grain surface, making the sand unsuitable for reuse. We have developed a process to reduce the total clay content from 12 % to as low as 2.2 % in waste foundry sand. Mechanical methods without any heat treatment can be used to reclaim green sand as opposed to current reclamation methods which involve burning the sand to around 800 °C. In this direction, three prototypes were developed during the course of this work; vertical fluidized bed, horizontal fluidized bed and two-stage mechanical attrition device. The cost of reclaimed sand is higher in case of fluidized bed based prototypes as opposed to two-stage attrition device, where it is less than half of the cost of the fresh sand. The experimental data generated on the two-stage attrition device under different conditions and the optimum set of design and operating parameters to get the best performance. Different strategies were studied for the reclamation of foundry sand. • The vertical fluidized bed prototype, which is based on the principle of particle-particle attrition, reduced clay content to 4.2 % from 12 %. • The horizontal fluidized bed brought down the clay content to as low as 2.2 % with higher operating cost. • Two-stage attrition device that uses particle-particle and particle ball attrition, combined with sieving, showed promising results, and a total clay content of up to 2.2 % was achieved in a cost-effective manner. Thus, it may be concluded that simple mechanical means of reclamation without heat treatment (∼800 °C) is promising and has a potential to improve economics of sand reclamation process, making reclamation economically viable for small and medium scale foundries. The two stage attrition device, which can reclaim up to 125 kg / hour of green sand, has been installed in Govt. Polytechnic, Kolhapur where it was tested for suitability & quality of the reclaimed sand. As far as field trial results are concerned, they were found to be satisfactory. Some foundries have started to use our reclaimed sand in Kolhapur foundry cluster. We conducted a survey of 100 foundries (small scale) in Kolhapur and surprisingly found that they are dumping WFS 600 TPM, which is a huge amount. Similarly, other foundries are also dumping WFS. According to the Institute of Indian Foundrymen (IIF, 2016), Indian foundries dump waste sand to the tune of 10 Million TPA. Disposal of WFS becomes one of the major challenges for foundry industries now days. It is also a big challenge for environmental concerns. The exiting unit (two stage mechanical attrition device) can reclaim the WFS at economical rate and make foundry process efficient. Use of reclaimed sand within the foundries will reduce the environmental concerns like health, occupational hazards, air and water pollution etc
About the Innovator
Address: Room No. 71-C, Hostel-12, Indian Institute of Technology Bombay, Mumbai-400076, India
City: Mumbai
State: Maharashtra
PIN Code 400076
Email: moiziitb@gmail.com
Contact No: 7506831990.0
Practice Details
Link: i. The two-stage attrition device involves only mechanical treatment and operation of this prototype is quite easy to handle
ii. Significant reduction of total clay from12 % to 2.2 %
iii. Only dead clay coating is removing from sand grains without affecting the sand properties
iv. The reclaimed sand is meeting the requirements of the foundries at nominal cost
(1 Rs/kg) which is quite remarkable and accepted by foundries
v. This mechanical reclamation process is environment-friendly as compared to conventional (thermal reclamation) method
News Link 5: