Development of a new chemical equilibrium and techno-economic model for the treatment of metal-polluted effluents by precipitation techniques

作者：Djedidi Zied; Bouda Medard; Ben Cheikh Ridha; Blais Jean Francois^*; Mercier Guy; Tyagi Rajeshwar Dayal

来源：Canadian Journal of Civil Engineering, 2011, 38(5): 593-604.

DOI：10.1139/L11-032

• metal
• precipitation
• sludge
• chemical equilibrium software
• hydroxide
• sulfide
• phosphate
• carbonate

A new computer program (PITEM) for the prediction of metal-finishing effluent treatment by precipitation techniques has been developed. PITEM integrates a mathematical model for the prediction of the sludge dewaterability and the volume of metallic sludge produced, and an economic module for the evaluation of the treatment costs of metal-rich effluent by precipitation techniques. It also integrates a chemical equilibrium model to predict the nature of the potential solid phase expected. PITEM is written with Visual Basic under the Microsoft Excel platform and is designed as easy-to-use software for industrial and (or) academic purposes. Nevertheless, PITEM database must be updated as in the context of future research to give it more accurate output data and a wider field use. Precipitation tests have been conducted in laboratory with multi-metallic solutions and polluted-soil leachate to compare wet sludge production with those predicted by the program after a mechanical solid-liquid separation by a pressure filtration. Simulation results show that predicted total solids (TS) are in agreement with those measured experimentally, except in the case of soil leachate precipitation with sulfide at pH 7.5 where TS predicted (23.1% w/w) is slightly higher (less water content) than the experimental value (18.4%) due to the formation of colloidal sulfur. Treatment costs ($/m(3)) estimated by the program for the four scenarios of soil leachate treatment by precipitation follow the ascending order: carbonates (Na(2)CO(3)) < sulfides (Na(2)S) < phosphates (Na(3)PO(4)) < hydroxides (NaOH). Limestone (carbonate) neutralization is the most cost-effective soil leachate treatment due to the good dewatering characteristics of the generated sludge (TS = 72.7%). This work demonstrates both the potential feasibility and the benefits involved in the use of chemical speciation models coupled with the sludge predictor tool to provide an economic forecast in the field of environmental water treatment.

• 出版日期2011-5