Search Documents

By G. X. Wang

The nonliving dried water hyacinth (E. crassipes (Mart.) Solms) roots were investigated for biosorption of cadmium and lead and other heavy metal ions in aqueous solutions. Dried water hyacinth roots, when suspended in solution, strongly and rapidly sorb several different metal ions. Factors such as reaction time, pH, initial concentration of metal ions, presence of other metal ions and biomass concentration were investigated. Metal ions, including Cd2+ and Pb2+, were bound to the root in a very pH-dependent manner, with the binding increasing after about pH 3. High levels of removal were obtained. The adsorption was shown to follow the generalized Langmuir adsorption equation. The relative affinity of the roots for lead is greater than for cadmium. The maximum sorptions of the roots were about 33 and 86 mg/g for cadmium and lead, respectively. Only 15-20 minutes were required for the process of uptake onto the biomass to occur. The batch sorption kinetics of the uptake of cadmium and lead can be described by an apparent first-order reversible reaction model. The roots could be regenerated after the metal ions were stripped. A solution of CaCl2 in acidic medium appeared to be the best eluant for desorbing the sequestered Cd and Pb completely at pH 3. The kinetics of the metal stripping process was quite rapid. Successful desorption of Cd and Pb from the biomass by acidic CaCl2 solutions revealed that the metal uptake phenomenon is reversible, implying physical sorption of Cd and Pb.

Jan 1, 1997

By M. M. Monte

A method for removing metallic mercury from contaminated tailing, using the flotation process, is described. In order to define some relevant parameters for the mercury flotation system, microflotation and electrophoretic mobility tests were carried out on (pure) metallic mercury in the presence of several surfactants. Based on the results obtained from fundamental studies a series of bench scale flotation experiments with mercury containing tailings from two wetland sites in Brasil were done. The results of microflotation tests with mercury showed that by using cetyl trimethyl ammonium bromide, an increase in mercury flotability is observed in the acid pH range, whereas in the presence of potassium oleate the highest mercury flotability was found in the alkaline pH region. The mercury flotability using potassium amyl xanthate was improved by the addition at sodium dithionate as an activator. The bench scale flotation tests with contaminated tailings from Poconé (brazilian wetland site) showed a recovery of 70% when sodium dithionate was used as activator and potassium amyl xanthate as collector. The resulting coefficient of separation is around 60%. However, the results of the flotation experiments with fine fractions from amalgamation tailings from Peixoto de Azevedo (brazilian wetland site) showed a low mercury recovery (32%).The results from this work suggest that since in the Poconé site tailings, the metallic mercury is not completely associated to the finer particles, the flotation process to recover the metallic mercury seems very promisor.

Jan 1, 1996

By Jerry D. St. Clair

A multidisciplinary team of scientists and engineers at Wont has been working to understand heavy metal contamination of DuPont process waste streams and technologies for abatement of these metals. As part of this effort, an extensive study was made of a specific waste stream of importance in DuPont's environmental commitment. This 200 gpm stream contains 5-5000 ppm of nickel plus a variety of inorganic and organic constituents. The chemical complexity of the waste rendered conventional. alkaline precipitation ineffective, and only through the simultaneous application of analytical characterization, fundamental chemical understanding, and process engineering did effective technical approaches emerge. In this instance, ion exchange, sulfide precipitation, and caustic digestion ultimately proved successful in reducing the nickel to below the 1 ppm target. The results of this study will be presented, along with key learnings about the process of solving heavy metal contamination problems.

Jan 1, 1994

By V. T. Panayotov, M. I. Panayotova

Wastewater from mining and mineral processing activities is often polluted by anion forming metals, such as molybdenum and chromium. Low cost materials, including zeolites, are studied for removing heavy metals from wastewater. It is widely accepted that natural zeolites are not effective in removing metals in anionic form. The paper presents study on use of metal modified natural clinoptilolite to remove Mo (VI) and Cr (VI) ions from model soft wastewater. Modification with Pb, Fe(III), Zn and Ba increases clinoptilolite uptake capacity with respect to Mo(VI) at low pH values of the water subjected to treatment, the efficiency decreasing in the order Pb > Fe(III) > Zn > Ba. Only lead-modified clinoptilolite shows high uptake of Mo(VI) in acidic, neutral and slightly alkaline conditions. Modification with Pb, Ba and Fe(III) increases zeolite uptake capacity with respect to Cr(VI) from neutral water. The effectiveness of Ba-modified zeolite decreases in slightly acidic water. Over 90 % uptake of initially available Cr(VI) is achieved by lead-modified clinoptilolite both under neutral and slightly acidic conditions. Increasing the initial pollutant concentrations increases the removed amount both of Cr(VI) and Mo(VI) for Pb-modified clinoptilolite. The findings could be a basis for using the natural clinoptilolite to remove in consecutive steps: firstly Pb(II) and/or Fe(III) ions and then loaded zeolite to be used for Mo (VI) and/or Cr(VI) removal. The kinetics of Mo(VI) uptake by CL-Ba, CL-Fe(III), CL-Pb, and CL-Zn is best described by the pseudo-first order kinetic equation. The kinetics of Cr(VI) removal by CL-Ba, CL-Fe (II), CL-Fe (III) and CL-Zn is best described by the pseudo-first order kinetic equation. Kinetics of Cr(VI) removal by CL-Pb obeys the equation for the first order irreversible reactions. Finding way to remove anions-pollutants from the mineral processing wastewater will render this industry more environmentally friendly and socially acceptable.

Jan 1, 2016

By Qingzhu Li

The adsorption process of Pb2+ from aqueous solutions by spent grains modified with Imol/L NaCI solution was investigated. The effects of solution pH, contact time, adsorbent concentration, initial Pb2+ concentration, particle size on Pb2+removal were also studied. The initial adsorption process was rapid and 90.35% of Pb2+ adsorption occurred within 30 min. The absorption equilibrium was obtained at 4h. When pH was 5.5, Pb2+ concentration in aqueous solutions decreased from the initial content of 20 mg/L to 0.0 I mg/L after 5 hours by application of IOg/L adsorbent at 25?C, Pb2+ removal efficiency reached up to 99.95% and the Pb2+ remaining in aqueous solutions was under China Sanitary Standard for Drinking Water (GB5749-85). Adsorption data fitted well with Lanf+muir and Freundlich models. However,Langmuir isotherm model was better to descnbe Pb- adsorplion than Freundhch model, mdlcatmg that the applicability of monolayer coverage of Pb2+ on the surface of adsorbent.

Jan 1, 2008

By M. De Ladurantaye-Noël, M. Laliberte

Selenium is widely present in the environment at usually low concentration. It is mostly present in the environment at higher oxidation states, i.e., as selenites and selenates (+4 and +6 oxidation states respectively). It is rarely present as selenides (-2 oxidation state) and almost never found as the element (0 oxidation state). Selenites and selenates are generally soluble in water, as such they cannot easily be removed from water by precipitation. Selenites can form insoluble surface complexes with metal oxides such as ferric hydrous oxide and manganese hydroxide, and can therefore be removed that way. However, it is not so common to find selenites in natural environments as it will quickly oxidize to selenate in aerobic conditions. Elemental selenium can also be produced from selenites or selenates by using a reduction process; the end product is a colloid that can be destabilized to be removed from water using the right chemistry. Because of their toxicity, selenides need to be handled with care, and if present, it can form insoluble metal salts or, at low pH, be emitted as H2Se, a noxious and highly toxic gas. The most favorable selenium forms for its removal are therefore selenite and elemental selenium. Organo-selenium species play a crucial part in understanding selenium toxicity. There are a great number of these species. Basically, any organic species that contains sulfur has an equivalent that contains selenium. Of particular interest is the substitution of sulfur by selenium in the two sulfur-bearing amino acids, cysteine and methionine, resulting in selenocysteine and selenomethionine. Methylseleninic acid (CH3SeO2H) is another organo-selenium specie which has been detected in water treated by biological processes and which is biologically active.

Feb 1, 2023

By J. R. Batista, J. C. Young

Leachates from gold heap-leaching mines may contain selenium concentrations as high as 2 mg/L. Previous studies report satisfactory selenium adsorption by activated alumina from relatively "clean" drinking waters. However, the findings of these studies cannot be directly applied to the treatment of mine leachate where other ions compete for the alumina adsorption sites. This study evaluated the adsorption of selenium from a mine leachate to develop design parameters for a full-scale activated alumina process. The study revealed that 68% of the selenium in the leachate could be removed by alumina at pH levels greater than 5.0. At pH levels less than 4, silica was poorly adsorbed by alumina, and selenium adsorption was improved. Silica adversely affected the selenium adsorption capacity.

Jan 1, 1998

By J. R. Batista

Leachates from gold heap-leaching mines contain selenium concentrations as high as 2 mg/L. Previous studies report satisfactory selenium adsorption by activated alumina when using relatively "clean" drinking waters. However, the findings of these studies cannot be directly applied to the treatment of mine leachate where other ions compete for the alumina adsorption sites. This study evaluated the adsorption of selenium from a mine leachate to develop design parameters for full-scale activated alumina processes. The study revealed that 68% of the selenium in the leachate could be removed by alumina at pH > 5.0. Silica adversely affected the selenium adsorption capacity. At pH values < 4, silica was poorly adsorbed by alumina and selenium adsorption was improved.

Jan 1, 1994

By Thomas D. Boyce

Minewater from many western U.S. uranium mines often contains radioisotopes in concentrations higher than permissible for discharge to unrestricted areas. .Radium 226 has the lowest permissible concentrations of all radioisotopes and usually greatly exceeds this limit in untreated effluents. This radionuclide is derived from the natural radioactive decay of uranium: [ ] The treating of minewater effluents has been studied previously (1) and the classical removal method for radium has been adsorption on barytes or freshly precipitated barium sulfate. This paper describes the removal of radium from minewater by utilizing a selective complexer based on a crosslinked organic polymer matrix.

Jan 1, 1982

By Michael Gebman, Jack Gerwick

"With the opening of the new San Francisco-Oakland Bay Bridge East Span, the former bridge and its caisson foundations are being demolished. Caisson foundations are in the path of a future shipping channel and therefore need removal down to the mudline 50 ft below water (MLLW). For the first caisson to be removed (E3) a mechanical demolition was performed above the waterline and an implosion was done for the remaining caisson down to mudline. Mechanical demolition consisted of excavators operating from either on top of the caisson, from work platforms or from barges. The demolition was implemented on a trial basis with a successful implosion on November 14, 2015. The work was conducted in an environmentally sensitive area, with measures taken to protect fish, marine mammals and birds. This demolition technique was cost effective, faster to execute, and had a better environmental impact then an alternative option. The demolition, measures implemented to protect the environment, outcome, and lessons learned are presented.INTRODUCTIONThe California Department of Transportation needed a cost effective and environmentally friendly solution for removal of the remaining San Francisco-Oakland Bay Bridge (former East Span) caisson foundations, starting with caisson E3. This was necessary to clear a future shipping channel. One option was to construct a steel cofferdam around the caisson to allow demolition in the dry down to the mudline. This option would take years to complete, be cost prohibitive, and its noise would disrupt aquatic life and birds throughout the cofferdam construction and demolition. An alternative option was implemented on a trial basis to conduct a mechanical demolition of the caisson above waterline along with an implosion of the remaining caisson down to mudline. This had the clear advantage as a cofferdam was not needed, and the demolition project duration would be approximately 6 months, instead of several years for the cofferdam option. The potential impact on aquatic life and birds from the implosion was a concern, as the location is environmentally sensitive; however, measures were implemented to minimize these impacts. As presented in this paper, this demolition option was implemented on a trial basis for Caisson E3. The technique succeeded and will now be used on the remaining caissons.BACKGROUND INFO ON CAISSON E3The reinforced concrete Caisson E3 is the largest caisson which supported the former East Span of the Bay Bridge. It was constructed in 1934, with the Bay Bridge opening in 1936. Figure 1 shows the project location. The caisson had a cell arrangement of 7 x 2 above the mudline. Below mudline, the caisson had a cell arrangement of 9 x 4. A structural transition was made between the 7 x 2 and 9 x 4 cell arrangements with buttress walls. All cells were flooded, as underwater openings were included in the original caisson walls to equalize the hydrostatic pressure. Figure 2 shows the caisson layout with limits for mechanical demolition and for the implosion."

Jan 1, 2016

Physical and chemical methods were investigated to tower thorium levels in Eneabba Ilmenite from the natural levels of 180-500 ppm to give Becher Process synthetic rutile with less than 100 ppm thorium. Chemlcal treatments, but not physical separations were successful. A pilot plant trial of a sodium hydroxide leach (25M NaOH at 75°C and 40 wt% solids for Ih) followed by a sulphuric acid leach (3M H2S04 at 90°C and 60 wt% solids for 211) confirmed that thorium could be removed to below 100 ppm. However, the activity of the ilmenite was not lowered to the same extent

Jan 1, 1996

The removal of tritium from tritiated water (-0.5 µCiIL) was studied by metallothermic reduction using aluminum. The influence of the three variables namely the aluminum powder amount, the NaOH concentration and the reaction time has been studied on the tritium activity reduction. The experimental results and statistical analysis showed that more than 85% of tritium can be removed from the tritiated water. Further work on the tritium recovery as well as efforts to totally decontaminate water by incorporating a cryogenic concept is currently pursued.

Jan 1, 1998

By N. I. Um

The coal bottom ash generated from coal-fired power plant accounted for approximately 5 mil-lion tons in Korea. Almost all of coal bottom ash was treated as reclamation of the landfill because of the content of unburned carbon. For recycling of coal bottom ash, effective removal of that is required. So, in this study, the removal of unburned carbon by flotation was studied with respect to adsorption ability in surface of a bubble in order to consider its application to recycle the coal bottom ash. The sample A, B and C were that the coal bottom ash contained 2.73%, 7.01% and 10.49% of the unburned carbon (UC) respectively. The column flotation was carried out for each time as the artificial injection of air at 10.0L/min flow rate and the reagents of 500g/ton kerosene and 80g/ton MIBC were used. The samples per water of 1.3 liters were from 0.5% to 4% (w/w.%). In the result of this study, the kinetic curves of unburned carbon adsorption from injected air bubbles were in-creased rapidly as equilibrium was approached; only 5 sec was needed from the sample A and B and 10 sec was from sample C. And the equilibrium isotherms of unburned carbon adsorbed by the infected air bubble from the sample B and C could appear the BET adsorption isotherm; MT = KMEEO/(EO-E)[EO+(K-1)E](K: adsorption affinity), but not the sample A that was not enough to express the adsorption curve.

Jan 1, 2014

By V. “Ram” Ramachandran

"In view of the increasing number of environmental regulations that have been promulgated all over the world in the last thirty years, non-ferrous smelters and refineries have had to learn and adapt to treating process bleed waste streams containing heavy metals. The result of such treatment invariably yields a gypsum-saturated solution containing salts such as alkali metal sulfates, chlorides and fluorides. Presence of anions such as sulfates, chlorides and fluorides in the discharge streams – presently not a major problem- are coming under increasing scrutiny and will have to be addressed in the near future. It is envisaged that discharge limits for sulfate ions will be in place in the near future. Treatment of brackish water to produce drinking water also results in brine streams containing alkali salts that have to be addressed for proper disposal. This paper reviews treatment options for such streams containing high levels of total dissolved solids with emphasis on sulfate removal. Areas covered would be: a) chemical treatment for removal of various constituents that make up the total dissolved solids b) processes for sulfate removal processes –thermal and non-thermal-to recover and reuse of treated water and c) brine use and treatment options.INTRODUCTIONThe rising cost of water and meeting the ever-changing stringent environmental discharge regulations make water recycling and reuse essential. The metallurgical industry has used water as a medium for dissolving and/or rejecting metals and chemicals in addition to removing thermal energy. Any excess process effluent is collected and sent to end-of-pipeline treatment and ultimately discharged to surface water for disposal under a permit. The conventional- and probably the cheapest way -of treating metal-bearing process effluent streams is lime neutralization followed by sulfide polishing for elimination of heavy metals to produce a stream that meets NPDES discharge limits. This results in a stream containing dissolved solids.These dissolved solids normally comprises of inorganic salts. The possible constituents are cations calcium, magnesium, sodium and potassium. The anions are sulfate, chloride, fluoride, nitrate, carbonate and bicarbonate. In addition to these constituents, the treated effluent streams contain very small amounts of heavy metals, oxyanions such as arsenites, arsenates, selenites and selenates. Process streams from gold operations contain residual cyanide. Small amounts of ammonium ions are also present in these streams based on the pH of the solution."

Jan 1, 2012

By Keith E. Forrester

This paper presents results of bench scale laboratory evaluation of a processes developed by FESI and Brookhaven National Laboratories for the extraction and recovery of Pb and other heavy metals from incinerator ash which was subsequently modified by FESI for the extraction and recovery of Pb from soils excavated from a FESI client scrap yard and battery breaking operation facility. The specific waste matrix presented within the paper is a battery acid contaminated surficial soil at 0" to 12" depth. The extraction method was found to be highly successful on the bench scale in generating a final post-extracted soil matrix which passed TCLP Pb regulatory limits and retained minimal Pb after aggressive extraction application. The paper findings at this time are brief, as a majority of the research results are currently being compiled and additional efforts are underway based upon initial screening findings.

Jan 1, 1995

Traditional in situ fan flow test methods under accepted standards require determinations to be made of both static pressures and total pressures during testing. This is to determine the resultant velocity pressures, which are vital in the accurate determination of the final fan airflow. These crucial velocity pressure (Vp) determinations are normally determined using simple manometric instrumentation such as an electronic manometer or an inclined liquid filled manometer. There is relatively little noise or fluctuation in the static pressure determinations and they can be quite easily and accurately recorded. There is almost always considerable fluctuation in the velocity pressure determinations though due to the highly turbulent and irregular velocity profile normally found in such in situ installations. This velocity turbulence means that the recording of such data is subject to random human error as the observer tries to average such fluctuations mentally during the observation period. Worse than this, and in the extreme, the recording of such velocity pressure data could actually easily be misreported if, for some reason, persons chose to do so.The author has devised a field method using highly accurate quartz crystal logging barometers to objectively record these velocity pressures. The method eliminates the ability to either mistakenly or intentionally misreport these crucial velocity pressures and is carried out in parallel with the recognised methodology, so result comparisons can be drawn. As such, a far greater level of confidence can be achieved in the final flow performance results than using the traditional more subjective method. Further to this it is difficult and almost impossible to refute the results using this ancillary substantiation method.The accurate determination of fan flows due to the impost of the carbon tax has taken on much more significance given the financial impacts in Australia at this time. The methodology detailed herein can be applied equally for both fan flow compliance testing and the verification of mine airflow data for greenhouse gas emission evaluations.The paper utilises the results of one 24-point pitot traverse to demonstrate the various findings. These include the very wide range of velocity pressures, which were logged at most of the measuring stations. It also illustrates how the method is utilised and compares the results derived from both this method and the more subjective traditional method along with the benefits of logging the velocity pressure results during the testing process.CITATION:Rowland, J A, 2013. Removing some subjectivity from traditional BS 848 and ISO 5802 in situ fan flow tests, in Proceedings The Australian Mine Ventilation Conference , pp 155-162 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By Robert McClure, Carlton Lehman

Rendering safe explosives in an urban environment presents a unique challenge due to the safety concerns and disruption to the general public. Potential damage to the surrounding homes, businesses, utilities and transportation infrastructure are some of the major concerns when planning the render-safe operation. Engineering controls to mitigate blast effects, such as damaging air over pressure levels, material ejection and ground borne vibration, need to be implemented as part of the operation. Monitoring of seismic and air overpressure during these operations are needed to protect against potential claims when controlled or unplanned detonations occur. Two recent render-safe operations conducted in and around urban environments dealt with deteriorated, sensitive dynamite and damaged blasting caps. Utilizing innovative neutralization chemicals and processes to render-safe the deteriorated dynamite, while protecting the general public, proved to be the safest, most environmentally responsible and cost-effective way to approach the problem. In both cases, the explosives, old dynamite and detonators were found in abandoned, unlocked magazines. The dynamite was in a significantly deteriorated state, which was evident due to the nitroglycerine found leaking in,around and under the dynamite cartridges. Iron wire permissible electric blasting caps were also found in a corroded condition with exposed explosives and un-shunted lead wires. With occupied buildings within 180 feet (54.86 meters) of the magazines, any procedure (e.g. transporting, countercharging, burning) that could potentially cause a detonation was not an option. In the event of an unplanned detonation during neutralization operations, several blast mitigation methods were employed to safeguard the site. This operation and a similar one with over 1,000 pounds of crushed and buried leaky dynamite were unique since all the explosives were rendered-safe and neutralized on site. The use of advanced neutralization products and filtering processes allowed for a safer, more environmentally responsible way to resolve the problem. The magazines and all residual solids and fluids were tested and confirmed by independent labs to have no explosives residues. The effluents were treated on site, tested and met safe levels, so they were disposed of at a local municipal wastewater facility.

By Robert McClure, Carlton Lehman

Rendering safe explosives in an urban environment presents a unique challenge due to the safety concerns and disruption to the general public. Potential damage to the surrounding homes, businesses, utilities and transportation infrastructure are some of the major concerns when planning the render-safe operation. Engineering controls to mitigate blast effects, such as damaging air over pressure levels, material ejection and ground borne vibration, need to be implemented as part of the operation. Monitoring of seismic and air overpressure during these operations are needed to protect against potential claims when controlled or unplanned detonations occur.

Feb 1, 2020

By George Carico

Research and related demonstration projects are being conducted in West Virginia on both existing and former coal surface mine lands to determine potential post-mine land re-use options that offer the greatest likelihood of future benefit and success. Examples of projects include renewable energy considerations that incorporate solar, wind, and/or biomass options, and contain components designed to educate business, government entities and the local community on renewable energy options and potential opportunities Multiple property re-use options are being researched and evaluated, based on site-specific conditions and characteristics, including infrastructure, local community needs and regional economic conditions. Re-use options being explored include innovative uses and needs, such as specialty housing, unique business and industrial needs, and an extensive variety of recreational and small business opportunities that best fit the specific needs of the local community and regional economic structure.

Aug 1, 2013

By J. Bakos

Solar Hydrogen Energy Corporation (SHEC Labs) recently constructed a pilot-plant to demonstrate a Dry Fuel Hydrogen Generation System that is powered primarily by sunlight focusing-mirrors. The pilot-plant consists of: A Solar Mirror Array and Advanced Solar Concentrator and Shutter System; and two thermo-catalytic reactors to convert Methane, Carbon Dioxide, and Water into Hydrogen. Results from the pilot study show that Solar Hydrogen generation is feasible and cost-competitive with traditional Hydrogen production. More than 95% of Hydrogen commercially produced today is by the Steam Methane Reformation (SMR) of natural gas, a process that liberates Carbon Dioxide to the atmosphere. The SMR process provides a net energy loss of 30 to 35% when converting from Methane to Hydrogen. Solar Hydrogen production provides a 14% net energy gain when converting Methane into Hydrogen since the energy used to drive the process is from the sun. The environmental benefits of generating Hydrogen using renewable energy include significant greenhouse gas and criteria air contaminant reductions.

Jan 1, 2005