Chromium, flotation

A number of different chromium collectors were also examined, including R84, which is a sulphonate collector as the primary collector, and amine acetate as the secondary collector was found to be effective for chromium flotation. The most critical parameter for selective chromium flotation was the pH. Selective chromium flotation occurs at a very narrow pH region, 1-2.5. Figure 25.12 shows the effect of pH on chromium flotation. 

The final flowsheet that was developed for chromium removal is shown in Figure 25.13. The concentrate was scrubbed with alkaline followed by desliming. The deslimed concentrate was subjected to chromium flotation followed by a single cleaning stage. 

The reagent scheme that was developed for chromium flotation is shown in Table 25.8. The pH control was achieved using nitric acid. The presence of nitric acid appeared to improve selectivity. The results obtained with HC1 and H2SC>4 were not as good as those achieved using HNO3. 

Final metallurgical results obtained using selective chromium flotation, from an ilmenite concentrate, are shown in Table 25.9. 

Figure 25.12 Effect of pH on chromium flotation from an ilmenite concentrate.

It should be noted that dissolved air flotation (DAF) is a more effective process for clarification.8-10 As shown in Appendix D, with an additional step of chromium reduction, the secondary treatment system effectively removed chromium (over 99%), copper (89%), cadmium (64%), lead (67%), and zinc (77%). 

FIGURE 6.1 Relationship between H2S03 and HS03 at various pH values. (Taken from Krofta, M. and Wang, L.K., Design of Innovative Flotation-Filtration Wastewater Treatment Systems for a Nickel-Chromium Plating Plant, U.S. Department of Commerce, National Technical Information Service, Springfield, VA, Technical Report PB-88-200522/AS, January 1984.)... 

Alternatively, hexavalent chromium can be reduced, precipitated, and floated by ferrous sulfide. By applying ferrous sulfide as a flotation aid to a plating waste with an initial hexavalent chromium concentration of 130 mg/L and total chromium concentration of 155 mg/L, an effluent quality of less than 0.05 mg/L of either chromium species can be achieved if a flotation-filtration wastewater treatment system is used.15... 

The newly developed flotation-filtration process involving the use of ferrous sulfide as a flotation aid offers a distinct advantage in the treatment of nickel-chromium plating wastewater that contains hexavalent chromium, nickel, iron, and other metals. 

There are two innovative flotation-filtration wastewater treatment systems that are technically feasible for the treatment of the nickel-chromium plating wastewater. 

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... 

Another innovative flotation-filtration wastewater treatment system adopts the innovative use of the chemical ferrous sulfide (FeS), which reduces the hexavalent chromium and allows separation of chromium hydroxide, nickel hydroxide, and ferric hydroxide in one single step at pH 8.5. Figure 6.7 illustrates the entire system. Again, a DAF-filtration clarifier plays the most important role in this wastewater treatment system. 

It is important to note that all flotation clarifiers63,64 may be used for treatment of nickel-chromium plating wastes regardless of their shapes (rectangular or circular) or manufacturers. A filtration unit is an optional step for final polishing. The treatment efficiency of separate flotation and filtration units65 will be similar to that of a combined flotation-filtration unit (Figure 6.8). 

The authors of this chapter are introducing a modem technology involving the use of flotation and filtration for treating nickel-chromium plating wastes. The authors are not endorsing any manufacturer s products. 

Another innovative flotation-filtration wastewater treatment system using FeS (Figures 6.7 and 6.8) is highly recommended if a totally new system is to be designed and installed for treatment of nickel-chromium plating wastewater. This system is extremely compact, easy to operate, and cost-effective. Treatment efficiency is also excellent. 

Medina, B.Y., Torem, M.L., and De Mesquita, L.M.S., Removal of chromium III from liquid effluent streams by precipitate flotation, in Waste Treatment, and Clean Technology, The Global Symposium on Recycling, REWAS 04, Vol. II, Gaballah, I., Mishra, B., Solosabal, R., and Tanaka, M., Eds., Madrid, Spain, September 26-29, 2004. 

Hiraide et al. [737] developed a multielement preconcentration technique for chromium (III), manganese (II), cobalt, nickel, copper (II), cadmium, and lead in artificial seawater using coprecipitation and flotation with indium hydroxide followed by ICP-AES. The metals are simultaneously coprecipitated with indium hydroxide adjusted to pH 9.5, with sodium hydroxide, ethano-lic solutions of sodium oleate and dodecyl sulfate added, and then floated to... 

Reagent practice in flotation of PGM from chromium-containing ores... 

The PGM carriers in this ore include a variety of PGM minerals (sperrilite) and its alloys. The main problems identified associated with processing this ore type were (a) poor concentrate grade, (b) low rate of PGM flotation, (c) excessive chromium reporting to the PGM concentrate and (d) high collector consumption. 

Significant improvement in chromium depression has been achieved using depressants from the KM series, representing mixtures of organic acid and low-molecular-weight acrylic acid mixtures. It is, therefore, possible to depress chromium during PGM flotation and at the same time reduce collector consumption. The relationship between the level of collector and level of KM3 depressant is shown in Table 18.9. 

Effect of type of collector on PGM rougher-scavenger flotation from high-chromium ores... 

The ilmenite production from heavy mineral sands exclusively utilizes a physical separation method using magnetic separation, gravity concentration and electrostatic separation. Flotation is practiced mainly for beneficiation of fine mineral sands containing rutile, ilmenite and zircon. The ilmenite that is produced in a number of operations in Western Australia, India and the USA is high in chromium, which makes the ilmenite unusable. This section discusses a new process that was developed for chromium removal from ilmenite concentrates. 

It was a known fact that flotation properties of both chromite and ilmenite are similar and they float equally well using either tall oil or amine collectors. Development testwork involved the examination of different ilmenite depressants and different chromium collectors. Depressants examined in this study included com starch, NaF and H2SiF6 at a low pH. Good ilmenite depression was achieved using H2SiF6, while the chromium was not affected. Similar results were achieved using NaF. 

Bulatovic, S., Chromium Removal from the Ilmenite Concentrate by Flotation from RZM Western Australia, Report of Investigation, 1993. 

Gao, P., Chen, X.M, Shen, F. and Chen, G. (2005) Removal of chromium (VI) from wastewater by combined electrocoagulation-electro flotation without a filter. Separ. Purif. Technol. 43, 117-123. 

Depends on the type of mineralization - contaminants from flotation agents of health concern include chromium, cresols, cyanide compounds, phenols and xanthates... 

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