REPORT OF PROCESSING TINMILL “CHEM TREAT” RINSE VIA THE ENVIRO-CLEAN PROCESS
A Comprehensive Report detailing the Effectiveness of Chromium Removal via the ENVIRO-CLEAN PROCESS; a Patented Technology.
National Steel is interested in significantly reducing the generation of hazardous waste from its finishing operation located at Portage, IN. Recently, Midwest replaced its cyanide based plating solution with a MSA based bath at the tinmill. This left chromium as the sole hazardous waste constituent generated from the plant. Also, a new acid pickle recycling service was installed which affected the chromium waste treatment process. Prior treatment practices consisted of blending of chrome waste with waste pickle acid. This change required National to purchase chromium reduction chemicals (meta-bisulfite) at an annual cost in excess of $300,000 per year. The treatment chemicals reduced the hexavalent chromium to a trivalent form, which was then precipitated at the chrome waste treatment plant. The resulting 35 million pounds per year of hazardous chromium sludge was disposed of on-site at Midwest’s captive land fill. This hazardous waste generation/disposal situation has existed for numerous years. A $10,000,000 capital appropriation is planned for a new chrome treatment plant to replace the outdated system. The pending new treatment plant is designed for a flow rate of 600 gpm. To add insult to injury, the planned new treatment plant maintains the status quo and does not offer Midwest any benefits, such as elimination of hazardous waste generation via chromium recovery and/or water recycle. Current waste treatment and disposal costs are approximately $1,800,000 per year which does not include National Steel’s corporate environmental liability for potential cleanup of the land fill.
Lewis Environmental Services (LES) has developed an innovative remediation approach to National Steel’s chromium waste streams utilizing the ENVIRO-CLEAN PROCESS. This new patented process adsorbs heavy metals from liquid waste streams onto a bed of granular activated carbon containing a proprietary chemical treatment. When the granular activated carbon is fully loaded, the concentrated heavy metals are stripped from the granular activated carbon and recovered with an innovative Electrolytic Metal Recovery (EMR) step. This process is superior to the existing state of art for treating heavy metal wastes from steel strip finishers because a recyclable EPA quality effluent is produced, no hazardous waste is generated and a salable metallic by-product is recovered.
This report will discuss the results obtained from a 90 day “chem treat” chrome removal trial conducted at National Steel’s Midwest Division plant located in Portage, IN. LES installed and operated a modular chrome removal system rated for 20 gpm. The unit processed a slip stream from the chem treat waste area and its operation matched the tin line production schedule. A flow schematic of the process is presented in Exhibit 1.0.
The next section will discuss the completed engineering study.
The overall objective of the engineering study was to demonstrate the effectiveness of the ENVIRO-CLEAN PROCESS to treat tinmill waste under continuous operating conditions over an extended period of time. This study was conducted with a commercial sized equipment package and at flow rate range(s) to verify the technologies performance capabilities to remove chrome under real in-plant conditions. The study’s objectives were: (1) monitor effluent quality over the course of the study to ensure it would met state and federal discharge limits, (2) verify that the effluent could be recycled back to the “chem treat” line and (3) determine the system’s level of chromium removal from the waste stream..
A daily sampling program was initiated with samples collected at 0700, 1600 and 2200 hours (military time). The sampling locations were: (1) the raw chem treat rinse line before it entered the system feed tank, (2) effluent – activated carbon filter #1 (EFF #1) and (3) effluent – activated carbon filter #2 (EFF #2). Analysis included: chromium (hexavalent and total), suspended solids, conductivity, total iron, oil and grease and pH. The unit was operated to match the tin line’s production schedule and outages.
Samples of the raw chem treat rinse were collected during each sampling period. The variations in chromium concentrations (total and hexavalent), conductivity, iron and pH were significant over the course of the trial. The three runs had widely varying concentrations for the above listed constituents. The ratio of hexavalent to total chromium concentration was nearly 1.0 over the course of the three runs, which indicated that hexavalent chromium was the primary species present. Table 1.0 list the constituent analysis (high, low and average) for the three runs.
Table 1.0 Raw Feed Analysis
Chrome Engineering Study
The chromium engineering study utilized a carbon removal system which consisted of a feed pump, tank, conductivity meter, pH controller, cartridge filters and two carbon adsorber units in series. Each filter contained 2,000 pounds of proprietary treated granular activated carbon. The system was skid mounted, prepiped and wired. A slip stream from the total chem treat waste stream was process by the Lewis system. The flowrate averaged approximately 15.0 gpm. The chem treat rinse stream was adjusted with 20% sulfuric acid or 20% liquid caustic to a pH range of 4.0 – 4.2. The treatment parameter values were based on positive results obtained from previous chromium removal projects. Lewis supplied a technician to operate the unit during daylight hours and Midwest line personnel collected samples on the back turns. Raw feed and effluent samples were collected and analyzed based on the above mentioned sampling program. The chem treat rinse stream was processed with minimal mechanical or process difficulties. Effluent samples were crystal clear and water white. Two carbon filters were replaced during the course of the trial. The test started on October 23, 2000 and was terminated on January 04, 2001. A total of 304,800 gallons were processed during the trial. Presented in Exhibit 2.0 is the complete analysis list of the feed and effluent samples, including date and collection time periods.
Chrome Trial Observations
This section will discuss the operational observations and performance of the chrome trial. The system was operated with two carbon filters in series. The system was shut down when the primary (lead) carbon filter exceeded its capacity to continue removing chrome from the rinse water stream while the secondary (polish) filter still produced an effluent hexavalent chromium concentration <0.01 mg/l; this completed a run. The next run continued with the secondary filter moved up to the primary (lead) position and a fresh carbon filter placed in the secondary (polish) position. Three runs were completed over the length of the study. The final effluent from Lewis’ carbon system was discharged to the chem treat clean water rinse section. No adverse effects developed with finished coil quality. Feed and effluent samples were collected each turn and analyzed for: total and hexavalent chrome, iron, conductivity and pH. Exhibit 2.0 list the individual test results for the various constituents observed over the three runs. Table 2.0 lists the maximum, minimum and average values for the various constituents over the length of the trial. Presented below are discussions highlighting the performance of each run.
Run #1 – October 23, 2000 through November 13, 2000. This run lasted seven turns and processed 58,800 gallons of raw chrome waste. This run had the highest average total chrome concentration over the entire study at 404 mg/l. The system maintained an average effluent hexavalent chromium concentration of <0.01 mg/l and average total chrome concentration of 0.16 mg/l. A small cartridge prefilter was installed upflow of the carbon adsorbers. It contained suspended solid material after several days. Samples of the suspended solids and spent activated carbon from the first replaced filter were collected and sent out for analysis.
Run #2 – November 11, 2000 through December 6, 2000 . During this 26 day period (including 5 day shutdown for Thanksgiving) the system operated 20 turns. A total of 144,000 gallons were processed during this time. This run had the lowest average raw chrome feed concentration and conductivity values observed over the three runs. The total chrome and conductivity values were 86.79 mg/l and 358µmhos/cm respectively. Also, a heavier coil coating oil was used for Kosher products during the second half of the run. Oil solids were observed in the raw waste stream and presented some processing difficulties.
Run #3 – December 11, 2000 through January 4, 2001. During this four week period (including 12 down days for Christmas thru New Years) the system operated 17 turns. A total of 102,000 gallons were processed during this time. This run exhibited the second highest average raw total chrome concentration of 173 mg/l.
Table 2.0 Summary of Constituent Analysis
|Date||pH||Total Chrome||Hex Chrome||Total Iron||pH||Total Chrome||Hex Chrome||Total Iron||Volume Treated|
Chrome Trial Results
This section will discuss the Lewis system’s final heavy metal effluent quality and chrome removal loading levels. Accurate determinations of these parameters were considered to be critical for the design of a full-scale system. The discussions are presented below:
Final Heavy Metal Effluent Quality
The ENVIRO-CLEAN PROCESS produced low concentration levels of total chrome and hexavalent chrome. Based on all three runs, the averaged effluent concentrations for total chrome and hexavalent chrome were 0.50 mg/l and 0.016 mg/l respectively. The carbon system’s removal efficiency was 99.0% for total chrome and 99.9% for hexavalent. This quality effluent would be suitable for direct discharge or possible recycle to a demineralizer system. Also, the carbon system was very effective in the capture of total iron with removal levels in the 99.4% range. This technology could be used to polish other iron bearing streams in the mill. Graphs of the heavy metal constituents are presented in Exhibits 4.0, 5.0 and 6.0 respectively.
Impact of Oil and Grease – There were 48 sampling periods with five final effluent samples exceeding the hexavalent chrome discharge level of 0.01 mg/l. Review of the operating data revealed that these excursions occurred during the second half of run #2, when a heavier coil coating oil was used for Kosher products. Considering no oil pretreatment process was in place, the carbon system processed normal coil coating oil exceptionally well, producing a low parts per billion effluent. Not withstanding, oil and grease pretreatment is a must for the full-scale system.
Suspended Solids Analysis – A sample of suspended solids material was collected from the cartridge filter(s) during run #1 and sent out for analysis. The sample was dark brown in color and assumed to be iron. After testing, it was determined that the solids were a combination of iron and chrome. Analysis revealed that the sample contained total iron and chrome concentrations of 11,800 mg/kg and 66,700 mg/kg respectively. It’s believed that the chrome solids precipitated during the electrolytic coating on the coils or chem treat process and ended up in the waste stream. Suspended solids pretreatment before the carbon filters will be required.
Chrome Removal Loading
The chrome removal loading for each run was calculated by dividing the total pounds of chrome removed that run by the pounds of carbon in the filter (2,000 lbs.). Over the three runs, the primary carbon filter adsorbed 186 lbs, 100 lbs and 149 lbs respectively as pure chrome. The chrome removal mass loadings percentages for runs #1, #2 and #3 were 9.3%, 5.0% and 7.5% respectively. A total of 304,800 gallons were processed. Based on past experience, the trial demonstrated excellent performance with chrome removal loadings of 5.0% – 9.3% while meeting <0.01 mg/l hexavalent chrome effluent concentrations. Chrome removal loadings of 5% – 7% are considered above average to superior levels for metal adsorption applications. Presented in Exhibit 3.0 is the chrome removal loading data.
Review of the operational data showed that for runs #1 and #3, the second filter adsorbed approximately 10.2 pounds of chrome in the polishing position. Run #2 with the heavier coating oil removed only 8.4 pounds of chrome, which was a 18% reduction. If the negative impact from the heavier oil was removed and assuming similar chrome removal loadings as in runs #1 and #3, run #2 would have processed an additional 94,000 – 117,000 gallons of chem treat waste, based on an average raw chrome feed concentration of 87 mg/l.
Spent Carbon Analysis – A sample of spent carbon was collected from the first replaced filter and sent to an outside firm for TCLP analysis. The spent carbon exhibited an oily smell and the carbon granules where tacky and stuck together. The carbon sample passed the TCLP test after washing with clean water (2 bed volumes) to remove high concentration chrome water from the carbon’s pores. The chrome concentration in the TCLP test solution was 1.7 mg/l; a pass is any chrome concentration <5.0 mg/l. Exhibit 7.0 lists the TCLP test results.