Low-molecular-weight polyacrylates

Sacrificial adsorption agents such as lignosulfonates (148—151) can be used to reduce the adsorption of more expensive polymers and surfactants. Other chemicals tested include poly(vinyl alcohol) (152), sulfonated poly(vinyl alcohol) (153), sulfonatedpoly(vinylpyrrohdinone) (153), low molecular weight polyacrylates (154), and sodium carbonate (155). 

In recent years, a new line of hydrophobic gangue depressants were developed, based on a mixture of guar gums and low-molecular-weight polyacrylates modified with organic acid, which are extremely effective. With the use of these depressants, the grade of the PGM concentrate could increase from 100 up to 40 g/t without any loss in recovery. 

The highest PGM recovery was achieved using collector PM443, which is an amine + ester-modified xanthate. Among the chromium slime depressants evaluated, modified mixtures of organic acids, RQ depressants and a low-molecular-weight polyacrylic acid + pyrophosphate mixture were there. The effect of different chromium depressants on chromium assays of the PGM concentrate are illustrated in Figure 18.7. 

As reported earlier (8j, polyxanthate dispersants can be prepared by reacting low molecular weight polyacrylic acid solutions with sodium hydroxide and carbon disulfide. Thus, to a 50-ml 1 percent... 

Biggs, S. and Healy, T.W, Electrosteric stabilization of colloidal zirconia with low molecular weight polyacrylic acid, J. Chem. Soc. Faraday Trans., 90, 3415, 1994. 

FIG. 8.24 Clay/oily soil redeposition of typical HDLDs. A, B, C, and D represent commercial liquid detergents, ranging from low-cost to premium brands, with and without the addition of a low-molecular-weight polyacrylate (pAA) homopolymer. 

During a study of the applicability of "spray" or "fog" evaporation to sea water desalination, it was found that this technique was particularly useful for scale deposition studies. Thus, test conditions are reproducible and heat transfer coefficients are very high, so that the effect of scale formation is readily apparent. Three novel methods for the control of scale deposits on the evaporating surfaces of a spray evaporator were explored. One involves the addition of small quantities of low molecular weight polyacrylic acid to the feed water, which prevents the formation of adherent scale. The methods are applicable under certain conditions to scales formed from sea water containing substantial amounts of calcium sulfate in addition to alkaline scale-forming substances. While spray evaporation appears to be of limited application in water desalination, the scale-control methods developed are probably applicable to other types of evaporator, particularly of the long-tube type. 

In one run, sodium sulfate and calcium chloride were added to a 200-gallon batch of sea water to give a sulfate concentration of 5200 p.p.m. and a calcium concentration of 640 p.p.m. An addition was made of 5 p.p.m. of low molecular weight polyacrylic acid and the treated sea water was evaporated under standard conditions. The over-all heat transfer coefficient averaged 3600 B.t.u./sq. ft. hr. ° F. for a 5-hour period, with no detectable falloff during the period, and the tube was found to be clean, except for the plastic film. In contrast, evaporation of a similar batch of calcium sulfate-enriched sea water, with no polyacrylic acid, resulted in a marked decrease in heat transfer coefficient to less than 800 B.t.u./sq. ft. hr. ° F. after 2 hours. 

A new additive, low molecular weight polyacrylic acid, has shown promise as an antiscale additive. It is suggested that scale prevention in this case is due to protection of the surface by a polymeric film, which alternately breaks away from the surface and regenerates, resulting in only slight resistance to heat flow. 

The authors express appreciation to H. R. C. Pratt and D. F. Kelsall for their help in the initiation and direction of this work. They also record their appreciation to A. E. Alexander of the University of Sydney and to G. H. Segall of Canadian Industries, Ltd., for providing the low molecular weight polyacrylic acid used in these experiments. Thanks are also due to E. S. Pilkington for assistance with the chemical analyses. 

Add in the low molecular weight polyacrylate with constant mixing. 

Add the low molecular weight polyacrylate polymer followed by the sodium hydroxide and sodium silicate. Mix until homogeneous. 

This is in fact what happens, although the base without polymers does precipitate earlier, i.e. at lower water hardnesses than the carbonate-rich version probably due to an earlier formation of Mg-silicate precipitate. The better performance of the low molecular weight polyacrylate is still visible in hard water. [14]... 

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