KR0100942 KAERI/RR-2085/2000 Development of the Removal Technology for Toxic Heavy Metal Ions by Surface-Modified Activated Carbon PLEASE BE AWARE THAT ALL OF THE MISSING PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK 2000 2001. 01. 26. uv - 1 - o ofc I. II. ofl Ufl CH] ^17^1-71 ^^H -B-7] 3L711 III. NaCl, NaNO3 - BET ^^ - 2 - all pH (2-10) ~0.4 g) :f-*HHH 4 *)2) iv. ^ (NaCl, NaOH, NaNO:i -Na 2. NaOH 0.1N 3. pH 2-10^1 AC, OAC, 4 ]•%•*}<>?{ OAC ^ OAC-Na^l OAC-Na OAC - 3 - 4. at-g-7] AC, OAC, OAC-Na^) xfl pH 3, 4, 5 ^^ OAC-Na>OAC»AC 5. pH7> OAC-Na XAD-16-TAR^l 6. pH 5 fe OAC^ll V. OAC-Na^l OAC-Na JL7\S\ -$-7} - 4 - SUMMARY I. Project Title Development of the Removal Technology for Toxic Heavy Metal Ions by Surface-Modified Activated Carbon II. Objective and Importance of the Project Organic ion exchange resins have been used to remove radionuclides such as uranium and cobalt ions in the radioactive liquid wastes generated from nuclear power plants or nuclear facilities. Organic resins, however, has some demerits such as radiation degradation and thermal instability. The development of an alternative inorganic adsorption material to the organic resins would eliminate these problems and greatly reduce the operation cost of wastewater treatment process with a high throughput. This new material can be used to remove uranium ions at a very low concentration in underground water for the fulfillment of regulatory criteria. In this project, a surface modified activated carbon is manufactured by a simple and cheap technique - acid/alkali solution treatment of normal activated carbon - and is tested to see its adsorption efficiency. Activated carbon has been widely used as a final cleaning material at the industrial wastewater treatment process before discharge to the environment. If the adsorption efficiency of activated carbon to remove the toxic heavy metals is enhanced by the surface modification technique, the operation cost and secondary waste volume can be significantly reduced. III. Scope and Contents of the Project Purpose of this project is to evaluate the adsorption capacities of both radionuclides and toxic heavy metals using double surface-modified activated carbon. Adsorbates are both uranium and cobalt ions as - 5 - representative of radionuclides and also lead, cadmium and chromium as toxic heavy metals in waste generated from industrial process. - First surface modification of activated carbon using nitric acid solution, and second surface modification with alkali solution(NaOH, NaCl, NaNO.3 solution) at various solution concentration. - Analysis of surface characteristics for modified-activated carbon by BET analysis, surface acidity and oxides measurements. Establishment of optimal condition for surface modification, based on adsorption efficiencies of uranium and cobalt. - Evaluation of adsorption efficiencies for both uranium, cobalt and toxic heavy metals under various experiment conditions, such as solution pH(2~10), initial concentration(12—50 ppm), carbon dosage(0.05~0.4 g) - Experiment to evaluate adsorption characteristics for the removal of uranium, cobalt and toxic heavy metals(single or multi-component) on three kinds of activated carbon in both batch reactor and fixed bed. - Comparison of the capacity factor(total treated waste volume/bed volume) using surface-modified activated carbon for the removal of toxic metals with that of the as-received activated carbon and commercial organic ion exchange resin, based on the results obtained from fixed bed runs. IV. Results of Project Adsorption capacities of both radionuclides(uranium, cobalt) and toxic heavy metals (lead, cadmium and chromium) using double surface-modified activated carbon in wide pH ranges are extensively evaluated. 1. Physical and chemical properties of surface-modified activated carbons, which are included three kinds of activated carbons (AC : as-received activated carbon, OAC : single surface-modified carbon, OAC-Na : double surface-modified carbon), are evaluated through BET analysis, surface acidity and oxides measurements. 2. It is established that optimal condition for the second surface modification of OAC is to use the mixed solution of both NaOH and - 6 - NaCl with total concentration of 0.1 N based on adsorption efficiencies of uranium and cobalt. 3. Variations in adsorption efficiencies of both radionuclides and toxic heavy metals on AC, OAC and OAONa were evaluated in wide pH ranges of 2 — 10. The adsorption capacity of both radionuclides and toxic heavy metals on OAC and OAC-Na is shown to be comparable to that of the AC in a low pH range. 4. Breakthrough behaviors of various metal ions in a column packed with three kinds of carbon were also characterized with respect to the variations of the influent pH and concentration. The adsorption capacity of the OAC-Na did stand a favorable comparison with that of AC and OAC. 5. Capacity factors of OAC-Na for the removal of various metal ions are superior to that of AC or OAC. Quantitative analysis of capacity factors for each ions showed that adsorption capacity of OAC-Na increased by 30 times for uranium, 60 times for cobalt, 9 times for lead, 30 times for cadmium, 3 times for chromium compared to that of AC at pH 5, respectively. Adsorption capacity of OAC-Na is also comparable to that of XAD-16-TAR used as commercial ion exchanged resin. V. Proposal for Applications The price of activated carbon is about 3 thousand won/kg and is very low compared to that of organic ion exchange resin (about 0.1 million won/kg). Hence the use of OAC-Na material seems very economical in the treatment of wastewater even if the cost of surface modification is considered. The OAC-Na activated carbon would efficiently remove toxic heavy metals in industrial wastewater as well as radionuclides in radioactive liquid waste. And the treatment cost and secondary waste volume would be greatly reduced compared to those in the treatment process adopting costly organic ion exchange resins or as-received activated carbons. The surface modified activated carbon can be utilized to - 7 - treat decontamination wastewater that is supposed to generate during the environment reclamation of uranium conversion facility at KAERI site. - 8 - Table 1. Physical properties of various carbons by BET-N2 analysis 34 Table 2. Experimental conditions for double treatment of OAC 34 Table 3. Acidic surface oxides of modified activated carbon 35 Table 4. Experimental conditions for fixed bed runs 40 — 9 — Fig. 1. Structure of activated carbon • 20 Fig. 2. Surface oxides on the carbon surface 22 Fig. 3. Process diagram of metal industrial waste included chromium compound 27 Fig. 4. Procedure for preparing the surface-modified activated carbon • • • 33 Fig. 5. Schematic diagram of a batch adsorber 38 Fig. 6. Schematic diagram for adsorption experiment in fixed bed 39 Fig. 7 Variation in adsorption efficiency of uranium and cobalt ion for various 2nd treated activated carbon [m/v -5(g/l), U=50ppm (pH=4.1), Cobalt=12ppm(pH=5.7)] 42 Fig. 8 Variation in adsorption efficiency of uranium ion for various 2nd treated activated carbon[m/v=1.25, 5(g/l), Co=50ppm] 43 Fig. 9 Variation in final pH after adsorption equilibrium of uranium and cobalt ion for various 2nd treated activated csrbon[m/v=5(g/l), U=50ppm(pH=4.1), Cobalt=12ppm(pH=5.7)] 44 Fig. 10 Variation in removal efficiency of uranium as a function of equilibrium pH by various surface-modified activated carbons at initial concentration of 50 ppm, m/v=1.25 46 Fig. 11 Variation in removal efficiency of cobalt as a function of equilibrium pH by various surface-modified activated carbons at initial concentration of 12 ppm, m/u=5 47 Fig. 12 Distribution of uranyl-hydroxyl complexes as a function of pH in pure water at 30 °C and total concentration of 10 ' mol// 49 Fig. 13 Fraction of cobalt ion species as a function of pH in pure water at 30°C and total concentration of 10 's mol// 50 - 10 - Fig. 14 Variation in removal efficiency of Pb as a function of equilibrium pH by various surface-modified activated carbons at initial concentration of 20 ppm, m/v=5 52 Fig. 15 Variation in removal efficiency of Cd as a function of equilibrium pH by various surface-modified activated carbons at initial concentration of 20 ppm, m/v=5 53 Fig. 16 Variation in removal efficiency of Cr as a function of equilibrium pH by various surface-modified activated carbons at initial concentration of 20 ppm, m/v=5 54 Fig. 17 Influence of adsorbent amount on uranium adsorption using various carbons at initial concentration of 100 ppm, pHo-3.1 56 Fig. 18 Effect of adsorbent dosage on Pb adsorption efficiency using various carbons at initial concentration of 20 ppm, pHo-3.1 57 Fig. 19 Effect of adsorbent dosage on Cd adsorption efficiency using various carbons at initial concentration of 20 ppm, pHo=2.7 58 Fig. 20 Effect of adsorbent dosage on Cr adsorption efficiency using various carbons at initial concentration of 20 ppm, pHo=2.75 59 Fig. 21 Effect of adsorbent dosage on Pb adsorption efficiency using various carbons at initial concentration of 90 ppm, pHo-4 60 Fig. 22 Effect of adsorbent dosage on Cd adsorption efficiency using various carbons at initial concentration of 90 ppm, pHo=4 61 Fig. 23 Effect of adsorbent dosage on Cr adsorption efficiency using various carbons at initial concentration of 96 ppm, pHo=4 62 Fig. 24 Uptake curves of uranium on OAC(pHo=3,4,5, Co=50 ppm) 64 Fig. 25 Uptake curves of uranium on Ac and OAC(pHo=3,4,5, Co-205 ppm) 65 Fig.