1. Field of the Invention
This invention relates generally to enhanced adsorbent particles, particularly particles that have been adsorbent enhanced by contacting with acid.
2. Background Art
Oxides of metals and certain non-metals are known to be useful for removing constituents from a gas or liquid stream by adsorbent mechanisms. For example, the use of activated alumina is considered to be an economical method for treating water for the removal of a variety of pollutants, gasses, and some liquids. Its highly porous structure allows for preferential adsorptive capacity for moisture and contaminants contained in gasses and some liquids. It is useful as a desiccant for gasses and vapors in the petroleum industry, and has also been used as a catalyst or catalyst-carrier, in chromatography and in water purification. Removal of contaminants such as phosphates by activated alumina are known in the art. See, for example, Yee, W., "Selective Removal of Mixed Phosphates by Activated Alumina," J. Amer. Waterworks Assoc., Vol. 58, pp. 239-247 (1966).
U.S. Pat. No. 4,795,735 to Liu et al. discloses an activated carbon/alumina composite and a process for producing the composite. The composite is prepared by blending powders of each of the activated carbon and activated alumina constituents. After the blend is thoroughly mixed, an aqueous solution is added to permit the activated alumina to rehydratably bond to the carbon particles. The amount of water added does not exceed that which prevents the mix from being extruded or agglomerated. After the water is added, the mix is subjected to a shaping or a forming process using extrusion, agglomeration, or pelletization to form a green body. The green body is then heated to a temperature of 25-100.degree. C. or higher. The composite may be strengthened by peptizing by adding nitric acid to the mixture. It is disclosed that the alumina can serve as the binder as well as the absorbent. This patent does not use a calcined alumina. Liu et al. discloses an amorphous alumina trihydrate powder, such as CP2 obtained from Alcoa and an amorphous alumina trihydrate powder such as CP-1 or CP-7, which are recited in U.S. Pat. No. 4,579,839, incorporated by reference in Liu et al. Liu et al.'s use of the term active refers to the surface water being dried and does not refer to a calcined particle. Liu et al. uses acid to strengthen the particle and not to enhance its adsorbent properties. Liu et al. uses an alumina precursor, which is an absorbent and not an adsorbent.
U.S. Pat. No. 3,360,134 to Pullen discloses a composition having adsorption and catalytic properties. Example 2 discloses an alumina hydrate formed by partially dehydrating alpha-alumina trihydrate in a rotary dryer by counter-current flow with a heated gas and an inlet temperature of about 1200.degree. F. and an outlet temperature of about 300.degree. F. The resulting product was washed with 5% sulfuric acid, rinsed with water and dried to about 2% free water content. Solid sucrose was mixed with the hydrate and the mixture heated. Example 4 discloses that the procedure of Example 2 was repeated except that calcined alumina was used. The product was unsuitable when calcined alumina was used. Thus, the acid washed product of Example 2 was not a calcined alumina.
U.S. Pat. No. 4,051,072 to Bedford et al. discloses a ceramic alumina that can be treated with very dilute acid to neutralize the free alkaline metal, principally Na.sub.2 O, to enable impregnation with catalytic material to a controlled depth of from at least 90 to about 250 microns. This patent does not use a crystallized aluminum oxide that has been calcined in accordance with the instant invention. This patent calcines the particle at a temperature of from about 1700.degree. F. to about 1860.degree. F. (927.degree. C. to 1016.degree. C.) to form a ceramic material, specifically what is referred to herein as an alpha alumina.
U.S. Pat. No. 5,242,879 to Abe et al. discloses that activated carbon materials, which have been subjected to carbonization and activation treatments, and then further subjected to an acid treatment and a heat treatment, have a high catalytic activity and are suitable as catalysts for the decomposition of hydrogen peroxide, hydrazines or other water pollutants such as organic acids, quaternary ammonium-salts, and sulfur-containing compounds. Acid is used to remove impurities and not to enhance the adsorbent features. This patent also does not utilize a particle of the instant invention.
Adsorbent particles of the prior art have not achieved the ability to remove particular contaminants from a liquid or gas stream, such as, for example, a waste stream or drinking water, to acceptably low levels. Additionally, the adsorbent particles of the prior art have not been able to bind tightly to particular contaminants so that the adsorbent particle/contaminant composition can be safely disposed of in a landfill. Thus, there has been a need in the art for adsorbents that have improved ability to adsorb particular materials, particularly contaminants from a gas or liquid stream, to thereby purify the stream. There has been a need in the art for the adsorbent particles to tightly bind to the adsorbed contaminant.