Using Aluminum Sludge Preparation Of Activated Alumina Adsorbent

The active alumina adsorbent had been prepared by using the wastesludge of aluminum factory in the thesis. As a project of integrated reusesolid waste, it has high social and economic benefit for the advantage oflow cost of raw materials and production without the necessity forpreparation aluminum hydroxide compare to the traditional preparationmethod. No patents and reports about the preparation of the activealumina adsorbent by using the waste sludge of aluminum factory hadbeen found through online retrieval both domestic and abroad. Therefore,it is the first work and possess of independent intellectual property in thisarea. The sludge which composed of high active superfine particles withhigh specific surface area is the waste residue comes from the processesof surface cleaning, alkali treatment and anodizing oxidation of thealuminum section surface. The major constituent of the sludge is the lowcrystallized alumina hydrate beside some amorphous solid. The content ofdifferent kinds of contaminants in the sludge meets the requirement ofpreparing the active alumina adsorbent. Two methods had been employed to prepare the active alumina. Theone is to calcinate the waste sludge directly. XRD technique and TEMtechniques have been used to characterize the crystalline phases andmicrostructures of each sample. The N2 adsorption method has beenemployed to determine the specific surface area and pore structure. Thecrystalline phase results showed that the crystalline phase meets therequirement when the calcination temperature was between 500℃ and800℃ . Heat treatment has relatively serious impact to the samples'specific surface area and pore structure. The specific surface area andpore volume first increase and then decrease with the increasing ofsintering time under 500℃. The specific surface area decreases with theincreasing of the sintering time under 600℃, 700℃ or 800℃. The porevolume first decreases and then increases a little too least with theincreasing of sintering time under 600℃. The pore volume increases alittle as the sintering time increases at 700℃ or 800℃. By syntheticalanalysis, the optimum calcination temperature is 600℃ and sinteringtime is 1h. Under such condition, the specific surface area is up to348m2/g and the pore volume reaches 0.55cm3/g which meet therequirement of the active alumina adsorbent. The TEM results showed theloose network structure of the samples formed by the stacking of theparticles with irregular size and shape. Another preparation method is introducing nitric acid as agglomerant,thus spherical shape samples with high mechanical strength can beprepared. The properties of each sample by adding different concentration,different amount of nitric acid, sintering at different temperature and timehad been discussed. The test methods are same to the first method. Theresults showed that nitric acid with certain concentration and amountcould improve the specific surface area but reduce the pore volume. Byanalysis, the best nitric acid concentration is 13% and amount is 31%, thebest calcination temperature is 600℃ and the best sintering time is 1h.The pore volume of the sample prepared under such condition was a littlelow but other properties could meet the requirement. The hole expansion additives can optimize the pore structure of theactive alumina. Ammonia bicarbonate and polyvinyl alcohol had beenemployed as the hole expansion additives to increase the pore volume forthe better performance and their effect had been evaluated. The resultshowed that a minimal increasing pore volume effectiveness couldobtained by using the ammonia bicarbonate but almost non effectivenessby using polyvinyl alcohol because of the dry gel structure of the wastesludge.