Adsorption and precipitation

In secondary operations, where chemicals are injected into hydrocarbon formations in conjunction with a chemical flooding process, polyamines are used to reduce the loss of injected chemicals to the formation by adsorption and precipitation (312). TEPA and other ethyleneamines are used with water-soluble polymeric thickeners in water—flood petroleum recovery operations to stabilize viscosity, mobiUty, and pH while imparting resistance to hydrolysis (313). 

Adsorption and precipitation are two commonly encountered sources of error in drug concentration. 

P. Somasundaran. Surfactant loss control in chemical flooding spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals—annual report for the reporting period September 30, 1992 to September 30, 1993. US DOE Fossil Energy Rep DOE/BC/14884-5, Columbia Univ, 1994. 

H. Zhang, E. J. Mackay, K. S. Sorbie, and P. Chen. Non-equilibriimi adsorption and precipitation of scale inhibitors corefloods and mathematical modelling. In Proceedings Volume, page 18 PR SPE Oil Gas Int Conf In China (Beijing, China, 11/7-11/10), 2000. 

Adsorption and Precipitation vs heterogeneous Nucleation and Surface Precipitation. There is not only a continuum between surface complexation (adsorption) and precipitation, but there is also obiously a continuum from heterogeneous nucleation to surface precipitation. The two models are two limiting cases for the initiation of precipitation. In the heterogeneous nucleation model, the interface is fixed and no mixing of ions occurs across the interface. As a consequence precipi-... 

Effluents from flooded mines are characterised by a more or less constant flow rate but a characteristic decrease of the contaminant load over time, resulting from the initial flush at the time of flooding and a prolonged tail due to the dilution of the mine water body by infiltration water inflow (which is partly overlain by dissolution, adsorption and precipitation processes within the mine)... 

Contaminant precipitation involves accumulation of a substance to form a new bulk solid phase. Sposito (1984) noted that both adsorption and precipitation imply a loss of material from the aqueous phase, but adsorption is inherently two-dimensional (occurring on the solid phase surface) while precipitation is inherently three-dimensional (occurring within pores and along solid phase boundaries). The chemical bonds that develop due to formation of the solid phase in both cases can be very similar. Moreover, mixtures of precipitates can result in heterogeneous solids with one component restricted to a thin outer layer, because of poor diffusion. Precipitate formation takes place when solubility limits are reached and occurs on a microscale between and within aggregates that constitute the subsurface solid phase. In the presence of lamellar charged particles with impurities, precipitation of cationic pollutants, for example, might occur even at concentrations below saturation (with respect to the theoretical solubility coefficient of the solvent). 

It should be noted that, in the natural subsurface solid phase, differentiation between adsorption and precipitation can be very difficult, because the new sohd phase may precipitate homogeneously onto the surface of an existing sohd phase. Weathering may provide host surfaces for the more stable phase into which they transform chemically. 

The most stable oxidation states of chromium in the subsurface environment are Cr(III) and Cr(VI), the latter being more toxic and more mobile. The oxidation of Cr(III) in subsurface aqueous solutions is possible in a medium characterized by the presence of Mn(IV) oxides. Eary and Rai (1987), however, state that the extent of Cr(III) oxidation may be limited by the adsorption of anionic Cr(VI) in acidic solutions and the adsorption and precipitation of various forms of Cr(OH). These authors also report a rapid quantitative stoichiometric reduction of aqueous Cr(VI) by aqueous Fe(ll), in a pH range covering the acidity variability in the subsurface even in oxygenated solutions. 

After filtration, samples for reactive Hg (Hg-R) and total dissolved Hg (Hg-T) were acidified with 0.5% HC1.47 BrCl is also often used to preserve samples intended for Hg-T determination. The acidification of samples to be used for Hg-R determination was not recommended by Parker and Bloom,85 especially those with high levels of dissolved organic carbon (DOC). DOC may coagulate after acidification of the solution, with concomitant adsorption and precipitation of Hg-R. Labile Hg (Hg-R) appears to be relatively stable (days to weeks) in filtered, unpreserved samples. 

In a similar study operated in a batch mode, Oguz [23] used gas concrete waste materials to remove F from aqueous solutions under varying experimental conditions such as solution pH and temperature. It was thought that the removal of fluoride by gas concrete took place both by adsorption and precipitation of Al3+ and Ca2+ salts. As a result of this study, it was concluded that wastes of gas concrete were an efficient adsorbent (about 96%) for the removal of fluoride ions from water. 

The method of soil suspensions extracts is based on metal desorption/dissolution processes, which primarily depend on the physico-chemical characteristics of the metals, selected soil properties and environmental conditions. Metal adsorption/ desorption and solubility studies are important in the characterization of metal mobility and availability in soils. Metals are, in fact, present within the soil system in different pools and can follow either adsorption and precipitation reactions or desorption and dissolution reactions (Selim and Sparks, 2001). The main factors affecting the relationship between the soluble/mobile and immobile metal pools are soil pH, redox potential, adsorption and exchange capacity, the ionic strength of soil pore water, competing ions and kinetic effects (e.g. contact time) (Evans, 1989 Impelhtteri et al., 2001 McBride, 1994 Sparks, 1995). 

Distribution, Transport, Adsorption, and Precipitation of Inorganic Phosphorus in the Genesee River... 

Acidification 5 ml of redistilled 6N hydrochloric acid is added for each hter of sample (added immediately upon collection to stabilize the solution from adsorption and precipitation). 

These quantitative methods must eventually detect potential chemical degradants, contaminants, and impurities induced by oxidation, deamidation, proteolysis, and disulfide exchange. Physical instability such as aggregation, denaturation, adsorption, and precipitation must also be detected and quantitated. 

Dissolution or precipitation reactions are generally slower than reactions among dissolved species, but it is quite difficult to generalize about rates of precipitation and dissolution (Stumm and Morgan, 1996). There is a lack of data concerning many geochemically important solid—solution reactions. Furthermore, there is not only a continuum between surface complexation (adsorption) and precipitation, but there is also obviously a continuum between heterogeneous nucleation and surface precipitation. 

Thompson, H. A., Parks, G. A., and Brown, G. E., Jr., (1999b). Dynamic interactions of dissolution, surface adsorption, and precipitation in an aging cobalt(II)-clay-water system. Geochim. Cosmochim. Acta 63, 1767-1779. 

Janusz, W.. Adsorption and precipitation processes in the cadmium oxide/aqueous NaCI or NaClO4 solution system, J. Colloid Interf. Sci., 145. 119, 1991. 

Janusz, W. et al., Adsorption and precipitation processes at cadmium oxide/sodium sulfate aqueous solution interface, J. Radioanal. Nucl. Chem., 174, 83, 1993. 

This chapter discusses the important mechanisms by which ions, whether present naturally in the soil or introduced by pollution, are sorbed by specific adsorption and precipitation, processes that are inherently less reversible than ion exchange. The chapter is intended to provide a fundamental basis for understanding inorganic cation and anion adsorption and precipitation, the reactions that limit solubility of many of the elements. 

---