Colloid deposition

The success or otherwise of the Ruckenstein and Prieve approximation has been tested by A. L. Smith (unpublished) for the process of colloidal deposition. He compared results from (43) with those obtained by performing the integration of the whole free energy profile. Results are collected in Table 3. It can be seen that the errors are no larger than 5%. 

Song, L., Johnson, P. R. Elimelech, M. 1994. Kinetics of colloid deposition onto heterogeneously charged surfaces in porous media. Environmental Science and Technology, 28, 1164-1171. 

Aizenberg J, Braun PV, Wiltzius P (2000) Patterned colloidal deposition controlled by electrostatic and capillary forces. Phys Rev Lett 84 2997-3000... 

Particulate fouling in RO is most likely to be colloidal due to the formation of a colloidal deposit layer on the membrane surface. Examples of colloidal partides... 

In RO, a colloidal deposit on the membrane introduces an additional resistance, Rf, and could also cause cake-enhanced concentration osmotic pressure (CEOP) [24]. The CEOP phenomenon is discussed in Section 6.3.4. Large-scale RO plants tend to be operated at a fixed production rate, requiring a fixed average flux. 

A labile phase of iron disulphide occurs in nature under the name melnikovite It is a black, finely divided substance which impregnates certain miocene clays in Russia, and differs in many respects from the black hydrated sulphide of iron usually found in black muds of lakes. In composition it corresponds to the formula FeS2. It is magnetic, and its true density is probably 4 2 to 4 3. Cold, dilute hydrochloric acid readily attacks it, evolving hydrogen sulphide. It has probably been derived from a colloidal deposit of an iron sulphide.3... 

The main reaction responsible for marble decay and damage to monuments is therefore the sulphation which occurs on the surface of these materials. Oxidation of SO2 to SO3 occurs by catalytic action due to surface impurities such as FeaO. , soot, colloidal deposits, CaS04 2H 0 already formed, humidity and also to sulphur oxidising bacteria. 

K. Aslan, S. N. Malyn, and C. D. Geddes. Angular-dependent metal-enhanced fluorescence from silver colloid-deposited films opportunity for angular-ratiometric surface assays The Analyst, 2007,132,1112-1121. 

Ma, H., Pedel, j., Fife, P. Johnson, W. P. 2009 Hemispheres-in-cell geometry to predict colloid deposition in porous media. Environmental Science and Technology 43, 8573-8579. 

Aizenberg, J., Braun, P.V., and Wiltzius, R, Patterned colloidal deposition conholled by electrostatic and capillary forces, Phys. Rev. Lett., 84, 2997, 2000. 

Fig. 13. The wall-jet apparatus for measuring the kinetics of colloidal deposition. The evanescent wave is scattered more strongly hy the deposited particles than those in the solution.

Li et al (1998, 1999) developed a technique that allows visual in-situ observation of colloids depositing on membranes. The technique is limited to transparent membranes, but allows the study of particle deposition and particle-membrane interactions. light microscopy was satisfactor) for super-micron particles, but fluorescence microscopy was required for sub-micron bacteria (0.5 am). 

As shown in Table 5.5 (No 1, 2, 3), HA concentration was varied from 5 to 20 mgL" DOC, but the increase in concentration had only a marginal effect on colloid rejection. The aggregates were not redispersed due to the addition of organics, which stabilised the particles in the OPS case. The deposition of DOC (results not shown) on the membrane increases with concentration, but colloid deposition is constant at about 90%. Organic rejection decreases with increased concentration. 

The amount M of solute or colloid deposited (in m on the membranes was calculated by using mass balance (see equation (6.1)), where Vf, Vr, and Vpi, are the volumes of feed, retentate and permeate (sample i), respectively, and cf, cr, and cpi the concentrations of feed, retentate and permeate. 

Table 7.43 and Table 7.44 show flux ratios, deposition, and rejection in the presence of colloids. Deposition is overall high and flux decline remains fully reversible. Rejection shows similar patterns for calcium and sodium as in the absence of colloids. DOC rejection is about 30% except at low FeCls concentration with OPS colloids. 

It t as found that the flux decline, even at critical fouling conditions is completely avoided by addition of ferric chloride. For large dosages (100 mgL FeCh), an osmotic pressure builds up and this reduces flux reversibly. The positive ferric hydroxide colloids deposit on the membrane and their charge appears to govern rejection. Cation rejection increases considerably, while the rejection of organics decreases. This demonstrates that the deposit on a fouled membrane can change rejection characteristics. 

---