Removal of Heavy Metals from Waste Waters by Natural and Na-Exchanged Bentonites

Batch sorption studies of Cr(III), Ni(II), Zn(II), Cu(II) and Cd(II) were conducted on Ca-bentonite and Na-bentonite to determine their retention capacities for these metal cations commonly present in the waste waters of galvanic industries. The Langmuir model was found to describe the sorption process well, offering maximum sorption capacities of 44.4 mg Cr/g, 6.32 mg Ni/g, 5.75 mg Zn/g, 7.72 mg Cu/g, 7.28 mg Cd/g on Ca-bentonite and 49.8 mg Cr/g, 24.2 mg Ni/g, 23.1 mg Zn/g, 30.0 mg Cu/g, 26.2 mg Cd/g on Na-bentonite. The use of Na-bentonite in the purification of waste waters from Ni, Cr and acid-Zn electroplating processes was an effective treatment in small-scale and in semi-industrial-scale tests. This proves the worth of this method as an alternative to existing methods. In contrast, Nabentonite was not effective in Zn sorption from cyanide-containing waste waters.