In many industrial processes, liquid solutions containing ions of various metals are formed depending on the technology used. These solutions are a side effect produced in both the metallurgical industry and in other industries. In the metallurgical industry, these solutions are an expected by product of manufacturing while in other industries these solutions will likely require special disposal. Proper processing of this wastewater enables the recovery of valuable metallic raw materials and prevents environment pollution by toxic metal ions.
Metals in wastewater may come from the galvanizing industry, tanning industry, paint, fertilizers, textiles and electrochemical processes. Cadmium is present in wastewater from the electroplating industry, dye production or nickel-cadmium batteries production. The sources of chromium are galvanizing, tanning, wood impregnation, textile and dye industries. The sources of copper are the metallurgical, dye and textile industries, pesticide production and fertilizers. Mercury finds its way into wastewater from the production of phosphoric acid, caustic soda, cellulose as well as from the production of pesticide products and the production of metallic mercury. Organic compounds of Mercury are also used in the production of fungicides. Lead is present in sewage from battery manufacturing, dyes and brass, and nickel finds its way into wastewater from the plating industry, paper production, refineries, steel plants and fertilizer factories.
One traditional method for removing heavy metals from wastewater is the sulfide method, which consists of precipitating heavy metals sulfides with sodium sulfide (Na2S) and further treating the wastewater with calcium hydroxide. The disadvantage with this method is the formation of heavy sedimentation and difficult filtering deposits. A better solution to use is sodium trithiocarbonate (Na2CS3). Studies have shown the use of sodium trithiocarbonate for the purification of various wastewater solutions containing cations of copper, zinc, iron, lead, chromium or arsenic are effective in precipitating heavy metals. An additional advantage of using sodium trithiocarbonate is the ability to remove heavy metals from oils and polar solvents to less than 1 pp. These metals can then be readily recovered from the remaining sludge.
Heavy metals can also be effectively removed by “green” biosorbents such as fungi biomass, sea algae, waste and agricultural residues, yeasts and bacteria. Many agricultural wastes such as fertilizers, tree bark or compost contain large amounts of lignin-cellulosic substances which can be used to remove heavy metals from sewage.
SAF Engineers offers solutions based on coagulation and filtration under pressure.