Removal of trace metals

If there was no metallie eontamination in the CMP wastewater, then, generally speaking, the waste eould be discharged directly to the POTW without any environmental issues or concern. This was demonstrated in the early days of semiconductor processing before copper interconnects became the industry standard. Since the introduction of copper processing, a whole new industry that provides waste treatment systems has blossomed. 

Removal of trace metals from liquid streams is not new and has been accomplished using as ion-exchange resin, seen in Fig. 19.2, which has been used in the water purification industry since the 1940s [13-16]. Most of the challenges associated with CMP waste treatment center around pretreating the waste stream prior to the trace metals removal step. Once the waste stream has been properly conditioned, it becomes a matter of removing the trace metal contaminants. For metals removal in CMP, cation resins are used. 

The ability of the resin to remove the target ion is dependent on the number of available ion-exchange sites (capacity), and selectivity, or relative propensity of the resin to capture specific contaminants. When considering common cations, their charge and relative selectivity are 

FIGURE 19.3 Schematic of a cation resin bead showing the polystyrene chains with sulfonic groups, the divinylbenzene cross-links, and the active sulfonic groups where the ion exchange occurs. Because the void spaces between the polymer chains and crosslinks contain water, the effective ion-exchange surface area of the bead is not limited to its outside diameter. 

Because low pH solutions will regenerate cation resins, the waste stream contacting the resin must be at a relatively neutral pH. If the pH falls, then regeneration could occur, and the trace metals captured on the resin will be released into the bulk fluid (at a higher concentration than the inlet stream due to the accumulation of metal ions in the bed). If the pH is too high, metal hydroxides could precipitate out of solution and permanently foul the resin. It is for this reason that the waste stream must be properly conditioned prior to contacting the resin. 

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Amuda, O.S., Amoo, I.A., Ipinmoroti, K.O., and Ajayi, O.O., Coaguation/flocculation process in the removal of trace metals present in industrial wastewater, Journal of Applied Sciences and Environmental Management, 10 (3), 159-162, 2006. 

The interaction and sorption of metal ions with metal oxide and clay surfaces has occupied the attention of chemists, soil scientists, and geochemists for decades (1-4). Transition metal oxides receiving particular emphasis have included various oxides of manganese and iron (5). Interest in sorption phenomena is promoted by the desire to better understand incorporation of metals into minerals, especially marine deposits ( ), the removal of trace metal pollutants and radionuclides from rivers and streams, via sorption and/or precipitation phenomena (1,6), and the deposition of metals on solid substrates in the preparation of catalysts (7,8). 

Removal of trace metals by adsorption is feasible in polar liquid streams, such as aqueous streams. One example is the removal of trace metal contaminants such as Rh+ lr+ Os+ Co+ Ni+ Mo+ V+ F+ Ti and Zn from an acetic acid... 

Lee, G., Bigham, J.M. Faure, G. 2002. Removal of trace metals by coprecipitation with Fe, Al and Mn from natural waters contaminated with acid mine drainage in the Ducktown Mining District, Tennessee. Applied Geochemistry, 17, 569 - 581. 

Availability of stationary phases Removal of trace metals... 

Florence, T.M. and Batley, G.E. (1976) Trace metal species in seawater. I. Removal of trace metals from seawater by a chelating resin. Talanta, 23, 179-186. 

Singer PC. 1974. Chemical processes for the removal of trace metals from drinking water. In SapoznikAR, O Connor JT, eds. Trace metals in water supplies Occurrence, significance, and control. Urbana, IL Engineering Publications Office, University of Illinois. 

A collection system is an array of piping under the manufacturing tools that accumulates the waste at a single point, such as a buffer or storage tank. The contents of the tank are then pumped to the unit operations of treatment system. The treatment system is a series of unit operations that modify the waste to produce a desired result, such as the removal of trace metals from the liquid stream. 

Schindler, P. W. Removal of trace metals from the oceans a zero order model. Thalassia Yugoslavica 11 (1/2), 101-111 (1975). 

Morris, A.W. (1986) Removal of trace metals in the very low salinity zone of the Tamar Estuary, England. The Science of the Total Environment 49, 297-304. 

The ion-exchange disks are available from a number of manufacturers (Table 6.1 and Appendix Product Guide). The disks typically have from 0.2 to 0.4 meq/disk (47 mm) exchange capacity. The disks manufactured by 3 M (Empore disks) are made from a styrene-divinylbenzene copolymer therefore, they do not have the problem of the silica-based disks with limited pH range. The Empore disks also come in a chelation disk for the removal of trace metals from solution, as well as in strong anion-exchange form (Fig. 6.1). 

Muzzarelli, R.A.A., Weckx, M., and Fillipini, O. 1989. Removal of trace metal ions from industrial waters, unclear effluents and drinking water, with the aid of cross-linked A-carboxymethyl... 

Continuous production of ultra pure water, removal of trace metal ions, etc. 

As iron is discussed as limiting nutrient for phytoplankton productivity of distinct oceanic regions (chapter 7.3) it is important to investigate the flux, degree of solubility and the bioavailability of the introduced iron into open ocean surface water. It has long been known that sorption onto suspended particles is highly efficient in the removal of trace metals from solution (Krauskopf 1956) resulting in a decrease of dissol-... 

Other procedures for the removal of trace metal contamination from the separation matrix will be discussed under the individual separation technique. 

Many studies have been made of the removal of trace-metal pollutants from water by a wide variety of natural products including soils and minerals. Although these materials have been basically utilized for water treatment rather than as an analytical step, some of them should prove useful for analysis if investigated more thoroughly. Specific examples employing these materials in-... 

Zemansky, G. M. (1974), Removal of Trace Metals During Conventional Water Treatment,/. Amer. Water Works Assoc., 66, 606-9. 

Fate and removal of trace metals/metalloids and fluoride from urban wastewater by membrane bioreactors pilot and full-scale experiences... 

Fate and removal of trace metals/metalloids and fluoride 221... 

OCCURRENCE, FATE AND REMOVAL OF TRACE METALS, METALLOIDS AND FLUORIDE... 

The results summarized in Table 12.1 show a general tendency in the removal of trace metals/ metalloids which follows the order As < B Se < Co < Ni < Pb < Zn < Cd < Cu < Ba < Mg < Cr < Fe operating conditions, the mixed hquor characteristics and the composition of municipal wastewater. Although the composition of municipal wastewater is rather stable in terms of organic content and macronutrients, its composition in trace metals can vary significantly in the order of ng L —jxg L. ... 

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