Resource detail

Title: Cadmium recovery and safe waste disposal
Organization:Sudarshan Chemical Industries Ltd
Source:Narang R K (Ed). 2009. Environment Best Practices: Industry Initiative. In series “Cleaner in Cheaper, Vol. 6”. New Delhi, India: The Energy and Resources Institute, 285pp.

Challenge: Sudarshan Chemicals Industry Ltd was established in 1968 and deals in pigments, pesticides as well as other agro chemicals. The company manufactures a very wide range of pigments, including conventional pigments, high performance pigments and effect pigments. Its main products include inorganic pigment, organic pigment, effect pigment and agro-chemicals. These have various applications such as coatings, inks, plastics, cosmetics, etc. One of the pigment products is manufactured from cadmium. The effluents released while making the same, contains cadmium in both soluble and insoluble forms. Cadmium is a hazardous pollutant, the accumulation of which in the human body can cause numerous diseases and ailments. Cadmium waste streams from the industries invariably end up in soil from where they are absorbed by plants and enter the food chain. It has no beneficial function in the human body and is a cumulative toxin. Hence there is a need to treat the waste before disposing it off.

Initiative: In order to minimize the toxicity and to ensure safe disposal, a process of waste recycling was put in place to reduce the concentration of cadmium. There is a pre-designed method for recovery of cadmium whereby Gypsum is used for flocculating and precipitating it from the effluent and the resultant gypsum sludge is then sent to secured landfills. Filter presses, tanks and pumps are employed and trained manpower is deployed for safe handling of the industrial waste. The process involves multiple stages and the resultant product is relatively free of the hazardous component.

The effluent is collected in a Collection Tank due to effect of gravity which is then neutralized with lime. The product is then subject to flocculation and then precipitation whereby cadmium is precipitated out along with gypsum. The neutralized and flocculated matter is sent to the primary clarifier where two distinct products are obtained. The underflow is subject to filter press to separate out the gypsum sludge. The overflow is sent to the secondary treatment plant and then for secondary clarification via equalization tank. The settled biomass obtained from the secondary clarifier is recycled back to the aeration tank which is relatively free of cadmium. The gypsum sludge is disposed off to secured landfills.

Outcome/Benefits: This methodology of waste recycling before disposal has not only significantly decreased the amount of hazardous chemicals dumped into the environment as cadmium content in gypsum sludge is reduced from 800 parts per million to less than 50; but has also proven to be extremely cost effective as cadmium is an expensive metal and its recovery results in cost benefit. There has been a net saving of Rs 6, 00,000/annum.

Thus hazardous effluents are dumped in a scientific environment-friendly way and there has been an increased awareness among employees about the need for safe waste management and disposal.