NOVEL PROCESS FOR PREPARATION OF SYNTHETIC HYDROTALCITE FROM INDUSTRIAL WASTE

摘要

Development of a novel process for preparation of synthetic hydrotalcite using three industrial wastes such as aluminium chloride waste-generated in any of reaction where anhydrous aluminium chloride is used as Leawis acid catalyst such as Freidel Craft reaction, bittern containing magnesium compounds generated in solar salt work using brines such as sea brine and subsoil brines containing magnesium, and ammonium carbonate solution generated in organic pigment industries such as producing copper pthalo cyanin green. The process involves preparation of aluminium precursor and removing metallic impurities present in Aluminium hydroxide prepared from aluminium chloride containing waste, preparation of magnesium precursor, mixing the precursors, hydrothermally treating the mixture and adding surface modifying agents followed by filtration and drying.

主权项

1. A process for preparation of hydrotalcite using industrial waste,
wherein the said process comprising the steps of; (A) preparing magnesium precursor
(i) diluting bittern with water to obtain a solution with 2-2.5% (w/v) magnesium ion concentration and clarifying the diluted bittern by treating with amounts of alum solution and caustic soda solution to precipitate aluminium and magnesium hydroxide in the range of 75-100 ppm and 200-300 ppm respectively;(ii) separating the settled hydroxides as obtained in step (i) and obtaining a clear solution of bittern with a magnesium ion concentration ranging between 2-2.5% (w/v);(iii) treating clear bittern as obtained in step (ii) with alkali carbonate selected from waste ammonium carbonate generated in pigment industries or recycled stream from step (xiv) while keeping mole ratio of carbonate ions to magnesium ions in the range of 1.1-1.4 at ambient temperature ranging between 25-40° C. for a period ranging between 30-60 minutes to obtain an aqueous slurry of a magnesium precursor;(iv) filtering the magnesium precursors as obtained in steps (iii) in the form of cake, and washing the cakes till washed liquor of magnesium precursor shows less than 0.1% (w/v) of chloride and sulphate respectively;(v) slurrying magnesium precursor into water, homogenizing the same and heating it up to 45° C.; (B) preparing aluminium precursor
(vi) reacting solution of aluminium chloride with treated ammonium carbonate waste or recycle stream comprising socium carbonate to prepare aluminium hydroxide;(vii) filtering aluminium hydoxide from slurry in step (vi) and washing with water to remove chloride impurities less than 0.1% (w/v);(viii) reacting wet cake of aluminium hydroxide prepared in step (vii) with alkali to produce sodium aluminate under continuous stirring at temperature ranging between 30-60° C. keeping 1.25 mole of Na2O/Al2O3 ions and additional alkali equivalent to Mg ions to be added as Magnesium carbonate to convert them all into Magnesium hydroxide;(ix) filtering the aluminium precursor prepared in (viii) above to remove all the insoluble metallic hydroxide and organic matter present in aluminum hydroxide prepared in step (vii);(x) mixing two precursors prepared in step (v) and (ix) to obtain mixed slurry of 3-5% (w/v) (on product basis) and stirring it at ambient temperature ranging between 35-45° C. for a period ranging between 3 to 4 hrs;(xi) heating the aged slurry in step (x) at temperature ranging between 140-150° C. for a period ranging between 4 to 5 hours in auto clave;(xii) cooling the slurry in step (xi) to temperature ranging between 70° C.-90° C., adding stearic acid of 4 to 4.5% (w/w on product basis) to a slurry with continuous stirring at temperature ranging between 70-90° C. for a period ranging between 15-25 min;(xiii) agitating the slurry obtained in step (xii) while allowing to cool to temperature ranging between 45-50° C., filtering the slurry and washing the cake till filtrate indicated pH of 8.5 to 10.0; wherein said filtrate comprises sodium carbonate having concentration in the range of 4-4.5% (w/v);(xiv) recycling the filtrate to step (iii) to prepare magnesium precursor or step (vi) to prepare aluminium hydroxide;(xv) drying the said wet cake as obtained in step (xiv) at temperature ranging between 100-110° C., pulverizing and sieving it to pass through 150-250 BSS mesh to obtain hydrophobic hydrotalcite in powder form;said steps (A) and (B) runs parallel or sequentially.