Steven R. Izatt

Challenges to achievement of metal sustainability in our high-tech society

Achievement of sustainability in metal life cycles from mining of virgin ore to consumer and industrial devices to end-of-life products requires greatly increased recycling rates and improved processing of metals using conventional and green chemistry technologies. Electronic and other high-tech products containing precious, toxic, and specialty metals usually have short lifetimes and low recycling rates. Products containing these metals generally are incinerated, discarded as waste in landfills, or dismantled in informal recycling using crude and environmentally irresponsible procedures. Low recycling rates of metals coupled with increasing demand for high-tech products containing them necessitate increased mining with attendant environmental, health, energy, water, and carbon-footprint consequences. In this tutorial review, challenges to achieving metal sustainability, including projected use of urban mining, in present high-tech society are presented; health, environmental, and economic incentives for various government, industry, and public stakeholders to improve metal sustainability are discussed; a case for technical improvements, including use of molecular recognition, in selective metal separation technology, especially for metal recovery from dilute feed stocks is given; and global consequences of continuing on the present path are examined.

Industrial applications of molecular recognition technology to separations of platinum group metals and selective removal of metal impurities from process streams

Green chemistry procedures using a novel process based on molecular recognition principles are described for the selective separation and recovery of metals in industrial processes. This process, termed molecular recognition technology (MRT), has the capability to make selective separations at various stages in metal life cycles. Results are given for individual platinum group metal separations, recycling of palladium from end-of-life products, copper purification by control of impurity bismuth concentration levels, and purification of H2SO4 for use in health-related applications by Hg removal to 0.1 mg L−1 concentration levels. In each case, the metals are selectively separated in pure form and can be recovered for reuse or environmentally safe disposal. High metal selectivity is obtained using a pre-designed ligand bonded chemically by a tether to a solid support, such as silica gel. Separations are performed in column mode using feed solutions containing the target metal in a matrix of acid and/or other metals. The target metal is selectively separated by the silica gel-bound ligand, leaving other solution components to go to the raffinate, where individual components can be recovered, if desired. Minimal waste is generated. Elution of the washed column with a small volume of eluent produces a concentrated eluate of pure target metal, which is easily separated in pure form. The MRT process uses innocuous wash and elution chemicals and no solvents. Metal recovery rather than dispersal into the commons is essential from a metal sustainability standpoint. A major benefit of metal recycling is reduction in the amount of virgin ore that must be mined to replace discarded metals. As metal use increases, conservation of this valuable metal resource increases in importance. Metal recycling rates are generally low. From end-of-life high-tech electronic products, they are in the 1–5% range. Separation and recovery results presented here show that green chemistry MRT processes have great promise in increasing metal sustainability in industrial processes.

Green Chemistry Principles Applied to the Selective Separation and Purification of Specialty Metals Using Molecular Recognition Technology

Green chemistry principles will be discussed, and examples will be given of the use of Molecular Recognition Technology (MRT) to selectively separate specialty metals such as cobalt, nickel, bismuth, rhenium, molybdenum, indium and germanium from various primary and secondary feed streams. Recovery of these metals has numerous advantages including (i) conservation of valuable resources, (ii) prevention of environmental damage, and (iii) elimination of capital and operating expenses due to re-processing or disposal of metal-bearing streams.