Reduction-precipitation system conventional

A modified reduction-flotation system (Figure 6.5) is very similar to the existing conventional reduction-precipitation system (Figure 6.4), except that a DAF clarifier [T-101F] is used for clarification15-57 instead of using a conventional sedimentation clarifier (Tank T-101, Figure 6.4). 

It should be noted that the chemical reactions of the conventional reduction-precipitation system (Figure 6.4) and the modified reduction-flotation system are identical. 

It is seen from Figure 6.7 that this system is much simpler, more cost-effective, and easier to operate in comparison with all other process systems discussed earlier. The treatment efficiency of the new flotation-filtration system is expected to be higher than that of the conventional reduction-precipitation system. The new flotation-filtration system also requires much less land space.15... 

Table 6.3 shows the characteristics of a typical effluent discharge from a conventional reduction-precipitation system. The effluent quality meets industrial pretreatment requirements. 

The treatment efficiencies of the two innovative flotation-filtration wastewater treatment systems (Figures 6.6 and 6.7) are expected to be higher than those of the conventional reduction-precipitation system. 

Figure 6.4 shows an example of an existing plating facility and its conventional reduction-precipitation wastewater treatment system in New Britain, TN.15... 

FIGURE 6.4 Conventional reduction-precipitation wastewater treatment system. 

The first system, shown in Figure 6.6, is identical to the conventional reduction-precipitation in chemistry (i.e., neutralization, chromium reduction, pH adjustment, metal hydroxide precipitation, and so on). However, a flotation-filtration clarifier (Tank T101SF, as shown in Figure 6.6) is used. The unit consists of rapid mixing, flocculation, high-rate DAF, and sand filtration.1557... 

The treatment efficiency of this system (Figure 6.6) is much higher than that of the conventional reduction-precipitation wastewater treatment system (Figure 6.4).15... 

The selected treatment option involves the reduction of hexavalent chromium to trivalent chromium either chemically or electrochemically. The reduced chromium can then be removed using a conventional precipitation-solids removal system. Alternative hexavalent chromium treatment techniques include chromium regeneration, electrodialysis, evaporation, and ion exchange.16... 

All of the above processes, in principle, afford the benefit of controlling the particle sizes of bimetallic systems that are eventually formed, whereas it may be more difficult to synthesize bimetallic colloids via traditional methods. Depending on the thermodynamic properties of the two metals, conventional catalyst preparation techniques (i.e., co-impregnation, co-precipitation) may result in the formation of a homogeneous alloy, segregation into pure monometallic phases, or a combination thereof. On the other hand, templating by dendrimers at least ensures that both metals are in close proximity with each other during complexation and after reduction. 

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