Grantee Research Project Results
2000 Progress Report: Spouted Bed Electrolytic Recovery of Metals for Source Reduction and Waste Minimization
EPA Grant Number: R826165Title: Spouted Bed Electrolytic Recovery of Metals for Source Reduction and Waste Minimization
Investigators: Calo, Joseph M.
Institution: Brown University
EPA Project Officer: Hahn, Intaek
Project Period: January 14, 1998 through January 13, 2001 (Extended to January 13, 2002)
Project Period Covered by this Report: January 14, 1999 through January 13, 2000
Project Amount: $291,499
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
This project is focused on the development of a new pollution prevention technology for "point source" recovery and recycling of metals from aqueous waste streams generated in a wide variety of large- and small-scale industries. The process concept is based on the use of spouted beds of metallized or metallic particles as cathodes for electrolytic recovery. These systems have considerable potential for providing superior performance in terms of current efficiency and current density, down to very low metal concentrations, with high recovery rates in comparison to other current technologies, as well as providing for facile recovery of metal in a high-quality form for recycling. The resultant devices are simple and inexpensive, with low maintenance costs.Progress Summary:
Prototype spouted bed electrolytic reactors (SBER), 12 inches, 7.5 inches, and 4 inches in diameter, were constructed. These reactors were used in various configurations of distributors and anodes to recover metals on metal particles or metallized glass spheres from a variety of metal ion-containing solutions selected to simulate those that may be found in a number of industries. In particular: (1) silver was successfully recovered in high-quality metallic form from both cyanide and noncyanide solutions at high rates and high current efficiencies, and silver was recovered from actual spent photographic fixer solution down to levels <1 ppm; (2) gold was recovered from gold cyanide solutions; (3) copper was successfully recovered from both copper cyanide and copper sulfate solutions; and (4) nickel was successfully recovered from nickel sulfate solutions.In general, it was found that the SBER approach was quite successful in recovering metals in a high-quality form from all the solutions investigated to date, at high current densities and current efficiencies. Observations indicate that different optimal operating conditions exist for each type of solution, depending on its particular electrochemistry.
It also was found that at longer contact times of bed particles with treated liquid solutions at low pH in the presence of dissolved oxygen, redissolution or "backstripping" of deposited metal can occur for certain metals. In essence, this operates as an opposing "back-reaction" for metals recovery. This phenomenon has been investigated to quantify its potential impact on net metal recovery in SBERs. In particular, "backstripping" experiments of copper and nickel in acidic sulfate solutions were conducted. It was concluded that "backstripping" effects could be easily circumvented or minimized in small-scale, point-source recovery operations. However, for larger-scale applications, such as copper recovery from semiconductor manufacturing operations, minimization of "backstripping" may have to be explicitly considered in reactor design and optimization.
A two-dimensional spouted bed apparatus has been constructed for the purpose of obtaining experimental data on particle entrainment and liquid flow distribution. The approach involves use of the data obtained from the two-dimensional apparatus to develop a numerical model of the spouted bed (first two-dimensional, and then three-dimensional) using FLUENT and its multiphase flow capabilities.
A Eulerian model has been developed to describe the behavior of the two-dimensional spouted bed. Results to date include solid particle recirculation rates as a function of inlet (jet) liquid flow rate. The observed behavior is nonmonotonic; that is, at low solids loadings, the solid particle recirculation rate increases with the liquid flow rate, and then decreases at higher bed loadings. This behavior is qualitatively similar for the bed with and without the conical particle distributor, although the effect is more marked with the distributor in place.
Future Activities:
The development of the SBER approach for point-source metals recovery will continue in the directions outlined above towards the goal of improving the understanding of these systems to the point where rational a priori engineering design will be possible.Journal Articles:
No journal articles submitted with this report: View all 15 publications for this projectSupplemental Keywords:
waste minimization, pollution prevention, waste metals recovery, particulate electrodes., Sustainable Industry/Business, Scientific Discipline, Industry Sectors, Manufacturing - NAIC 31-33, Chemical Engineering, Engineering, Environmental Chemistry, cleaner production/pollution prevention, chemical use efficiency, source reduction, waste minimization, chemical precipitation processes, cyanide solutions, pollution prevention, green technology, metal recovery , waste streams, circuit board manufacturing, waste reduction, cleaner production, spouted bed electrolytic recoveryProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.