Environment Remediation Research Managing Metals, Carbon & Excess Nutrients
1. Phosphorus Adsorption
1.1 Cost-Effective Phosphorus Removal from Secondary Wastewater Effluent through Mineral Adsorption. Executive Summary
Loadings of phosphorus (P) in wastewater discharges are detrimental to surface water quality. The addition of P to surface waters leads to increased production of algae and rooted plant biomass and reduced water clarity. While natural and constructed wetland systems have been used for secondary treatment of municipal wastewater, they have not proven effective at reducing the soluble phosphorus (SP) from wastewater discharges. Recent research, however, has indicated that a constructed subsurface-flow wetland using a substrate efficient at adsorbing P could successfully reduce SP. Laboratory experiments with wollastonite, a calcium metasilicate mineral, demonstrated that SP concentrations averaging 6 mg/l in secondary treated wastewater could be reduced to less than 0.8 mg/l provided the hydraulic residence time (the contact time of the wastewater with the wollastonite) is more than 43 hours.
Laboratory and pilot facility results indicate that a subsurface-flow constructed wetland with a surface area of approximately 1.4 acres and a wollastonite depth of 2.5 feet should be adequate to remove 90% of the incoming SP from the waste water treatment plant. Since a constructed wetland at this site could use gravity flow, operation and maintenance costs should be reasonable.
See related topics and documents: 36_Phos_Mineral_Adsorption_1999.pdf
1.2 Town of Willsboro Explores Innovative Technologies: Abstract
Directly addressing an action called for in Opportunities for Action, the Town of Willsboro, NY and scientists from Cornell University recently completed a pilot study of a promising new technology that removes phosphorus from wastewater. The new method is potentially more cost-effective than traditional chemical phosphorus removal techniques. In the study, treated wastewater from the Willsboro treatment plant was passed through a small experimental wetland containing wollastonite, a locally mined mineral. The wollastonite removed a significant amount of the phosphorus from the wastewater passed through the wetland. Willsboro has applied to the New York Clean Water/Air Bond Act for funding to test the technology at a larger scale. The pilot study was funded in part through an LCBP grant.
See related topics and documents: P reduction from Wollastonite.pdf
1.3 Phosphorus removal by wollastonite: A constructed wetland substrate
Abstract: Wollastonite, a calcium metasilicate mineral mined in upstate New York, is an ideal substrate for constructed wetland ecosystems for removing soluble phosphorus from secondary wastewater. Design parameters, required for designing a full-scale constructed wetland, were measured in vertical upflow columns with hydraulic residence times varying from 15 to 180 h. Secondary wastewater was pumped vertically upward through eleven soil columns, 1.5 m in length and 15 cm in diameter and influent and effluent concentrations of soluble phosphorus were monitored for up to 411 days. Greater than 80% removal (up to 96%) was observed in nine out of 11 columns and effluent concentrations of soluble phosphorus ranged from 0.14 to 0.50 mg:l (averaging 0.28 mg:l) when the residence time was \40 h. Columns with a decreased residence time averaged 39% removal. A direct relationship between residence time and soluble phosphorus removal was established.
See related topics and documents: Phosphorus removal by wollastonite- A constructed wetland substrate.pdf
1.4 Evaluation Of Filter Media For Treating Stormwater Runoff
Abstract: In dry retention ponds, urban runoff contaminants are removed by numerous physical, biological and chemical processes as water percolates through the bottom and side wall soils. Many of these same mechanisms are harnessed in engineered devices, such as sand filters, that intercept runoff either before entering or after leaving a detention facility. We conducted two experiments to examine the ability of filter devices to remove total suspended solids (TSS), total phosphorus (TP), and selected dissolved metals from urban runoff. In the first study, triplicate mesocosm sand filters situated next to a wet detention pond were loaded once weekly with urban runoff that had been augmented (spiked) with P and metals. Performance of the filters initially was good, but for several constituents removal effectiveness declined with time. During a 16 month period the filter was moderately effective at removing TSS, copper and phosphorus, and less effective for removing cadmium and nickel. In a second experiment, we used laboratory columns to test the effectiveness of quartz sand, peat, limerock and wollastonite (a mine tailing) as filter media for removing these same contaminants. Peat was the most effective filter matrix for metal removal and wollastonite was the most effective for TP removal. Filter matrices other than sand therefore may prove useful for selected urban runoff treatment applications.
See related topics and documents: An Evaluation of Filter Media.pdf
1.5 Evaluation Of Specialized Permeable Media For Phosphorus Removal
Overview: Excessive loadings of phosphorus from anthropogenic sources can cause the development of algal blooms that eventually decompose allowing an increase in the consumption of dissolved oxygen in water bodies. In reaction to this environmental concern, low cost approaches in lieu of conventional methods have been examined as viable alternatives. Engineered treatment wetlands are a cheap, efficient alternative to traditional methods in the removal of conventional pollutants from wastewater.
Observation: the four columns consisted of 100, 95, 90 and 80 percent wollastonite with the remainder comprised of filtralite-P. On average, 92% removal of soluble phosphorus was achieved in the wollastonite only treatment column operated at an hydraulic application rate of 0.91 m3/m2-day.
See related topics and documents: The Evaluation Of Specialized Permeable Media For Phosphorus Removal _ Ph.D.pdf
1.6 Determining Design Parameters For Recovery For Aquaculture Wastewater Using Sand Beds
Abstract: Design information for the use of sand beds to remove suspended solids from wastewater discharged from recirculating aquaculture systems (RAS) was developed. Wastewater from a commercial RAS tilapia farm with 2% total solids and 1.6% total suspended solids (TSS) was applied to sand columns to determine infiltration rates and phosphorus capture. Various hydraulic loading rates and drying periods between application events were evaluated. Infiltration rates stabilized after five application events to 3.5 cm/day (S.D. = 1.7). Practically, all suspended solids were captured at the top of the columns, creating the primary resistance to infiltration. Concrete sand removed approximately 93% of the soluble phosphorous in the wastewater and wollastonite, an economical aggregate alternative to sand, removed at least 98%. A modified Darcy equation is presented to predict infiltration based upon TSS and the number of sequential applications.
See related topics and documents: Wollastonite-treatment.pdf
1.7 Phosphate sorption capacities of different substrates in view of application in water treatment systems for ponds
Abstract: Several substrates have been examined on their phosphate sorption capacity. Wollastonite powder exhibited the highest removal capacity. At all phosphate concentrations, the removal was above 82%, with a maximum of almost 96%. The uptake rate was high in the first hour of the batch test and increased with increasing concentration. The wollastonite granules did not take up phosphate at concentrations below 2 mgP/l. Other materials (ceramic cylinders with active micro-organisms, porphyry and scoria) that were studied did not exhibit phosphate uptake. From this study , it is concluded that wollastonite powder has the highest phosphate removing capacity, but that slag is better suited for application in a skimmer, placed as a pretreatment in the water treatment loop of the pond, as the material is coarser.
See related topics and documents: WWC2010-Van_Hulle-wetland.R1d.pdf
2. Metals Remediation
2.1 Minerals in Waste Remediation
Abstract: Industrial minerals, with or without modification, are useful for removing and sequestering harmful waste products.
Conclusions: The use of industrial minerals in environmental remediation is likely to grow with the growth of legislation, especially during the presidency of Barak Obama. The minerals most likely to be affected by such trends will be limestone, lime, magnesium hydrate, micas, clays, zeolites, activated carbon, graphite, wollastonite, diopside and synthetic silicas.
See related topics and documents: Long-term interaction of wollastonite with acid mine water and effects on arsenic and metal removal.pdf
2.2 Long-term interaction of wollastonite with acid mine water and effects on arsenic and metal removal
Abstract: This paper reports the results of a laboratory experiment conducted to investigate the effects of wollastonite dissolution on removal of potentially toxic trace elements from stream waters affected by acid mine drainage (AMD). Nearly pure wollastonite was treated with natural acid mine water (pH 2.1) for different lengths of time ( 15, 30, 50 and 80 days). The compositional and textural characterization of the solid reaction products suggests that wollastonite was incongruently dissolved leaving a residual amorphous silica-rich phase that preserved the prismatic morphology of the parent wollastonite. The release of Ca into solution resulted in a pH increase from 2.1 to 3.5, and subsequent precipitation of gypsum as well as poorly crystallized Fe-Al oxy-hydroxides and oxy-hydroxysulfates whose components derived from the AMD solution. A geochemical modeling approach of the wollastonite-AMD interaction using the PHREEQC code indicated supersaturation with respect to schwertmannite (saturation index= 10.7-15.7), jarosite (SI = 8.7-10.2), alunite (SI = 5.1), goethite (SI = 4.7) and jurbanite (SI 2.2). These secondary phases developed a thin coating on the reacted wollastonite surface, readily cracked and flaked off upon drying, that acted as a sink for trace elements, especially As, Cu and Zn, as indicated by their enrichment relative to the starting wollastonite. At such low pH values, adsorption of As oxyanion~ on the positively charged solid particles and coprecipitation of metals (mainly Cu and Zn) with the newly formed Fe oxy-hydroxides and oxy-hydroxysulfates seem to be the dominant processes controlling the removal of trace elements.
See related topics and documents: Long-term interaction of wollastonite with acid mine water and effects on arsenic and metal removal.pdf
2.3 Reclamation of Cr(VI) rich water and wastewater by wollastonite
Abstract: Chromium exists in two forms mainly Cr(III) and Cr(VI) and out of the two forms the later one is highly toxic and is documented as high priority pollutant. It has attracted the attention of the scientific workers worldwide. The present work was addressed to the use of clay mineral, wollastonite in order to provide an economically viable treatment of Cr(VI) containing aqueous solutions and industrial effluents. The removal of chromium is found to be concentration dependent. The removal increased from 47.4 to 69.5% by decreasing the concentration from 2.0×10−4 to 0.5×10−4M at pH 2.5, 0.01M NaClO4 ionic strength, 100 um adsorbent particle diameter and 30 ◦C temperature. Rate of uptake of Cr(VI) was found to be 3.0×10−2 min−1 under optimum conditions and the process is governed by first order kinetic equation. The process of Cr(VI) removal from aqueous solutions and wastewater involves intraparticle diffusion and the coefficient of intraparticle diffusion, D, was found to be 3.5×10−4 cm2 s−1 under favourable conditions. Thermodynamic parameters for the process of removal have also been calculated to understand the process better.
Conclusions: The studies on the removal of Cr(VI) by adsorption on wollastonite provide important information. Broadly the conclusions may be drawn as follows:
- (i) The adsorbent shows significant removal of Cr(VI) from aqueous solutions and higher removal has been obtained at low concentration ranges.
- (ii) The process of removal follows first order rate kinetics.
- (iii) Intraparticle diffusion plays an important role in Cr(VI) removal.
- (iv) Higher removal is obtained at low pH ranges.
- (v) Temperature studies show that the unlike most adsorption processes, the present process is endothermic in nature and thus, higher removal can be obtained at higher temperature.
Further, as the adsorbent is naturally available, it incurs no extra financial burden on the users and hence it can always be recommended for the treatment of Cr(VI) containing waters and wastewaters.
See related topics and documents: Reclamation of Cr(VI) rich water and wastewater by wollastonite.pdf
2.4 Use Of Wollastonite In The Removal Of Ni(Ii) From Aqueous Solutions
Abstract: The ability of wollastonite to adsorb Ni (II) from water has been carried out. A removal of 92% of Ni (II) with 20 g L -I of adsorbent was observed at 50 mg L -I adsorbate concentration, 6.5 pH and 30 °C. The process follows a first order rate kinetics with diffusion controlled nature and the data fits the Langmuir adsorption isotherm. Removal of Ni increases from 10 to 92% with the rise of pH from 3.0 to 8.0 and thereafter it remains almost unchanged. This change has been explained on the basis of aqueous-complex formation and the subsequent acid base dissociation at the solid-solution interface.
- Higher uptakes (92% of Ni (II)) from aqueous solution is possible using wollastonite as an adsorbent provided the initial concentration of the Ni (II) in the effluent is low. This is our important finding in the light of industrial applications.
- The adsorption follows the first order kinetics.
- The adsorption data fits the rearranged Langmuir isotherm under the present experimental conditions.
- pH has been found to be a master variable controlling the adsorption of Ni (II) by the oxides present in wollastonite. The adsorption behavior can be predicted (qmax) from a knowledge of CNi/CHn ratio, where ‘n’ is equal to 2.2 under the present conditions. The adsorption is maximum around pH 8.0 onwards and it has been concluded that surface complexation involving H + exchange and chemical precipitation contribute towards maximum uptake.
- The data, thus obtained, may prove to be a blue chip for Ni (II) removal from wastewater using batch or strirred-tank flow reactors.
See related topics and documents: Use of Wollastonite in the Removal of Ni(II) from Aqueous Solutions.pdf
2.5 Use of Wollastonite for Tailing Waste Management Enriched in Mn (II) and Zn (II)
Abstract: This paper deals the study of use of wollastonite for the treatment of tailing wastes enriched in Mn(II) and Zn(II). The efficiency of wollastonite was tested at different concentrations and temperatures at suitable pH of the system. It was found that low concentration favors the uptake of adsorbate species. However effect of temperature varies with the nature of adsorbate Species The process of uptake follows a first order adsorption rate kinetics and obeys Langmuir model of adsorption isotherm. The removal process has also been found to be partially diffusion controlled and mass transfer co-efficient have been determined to explain the mechanism of adsorption. The effect of pH has been discussed incorporating various surface site reactions. A generalized empirical models is proposed for different initial concentrations and temperatures.
This study indicate that wollastonite may be used as an efficient adsorbent for the treatment of Mn(II) and Zn(II) bearing waste streams. Wollastonite has a good adsorption capacity for Mn(II) and significant for Zn(II) . The fitness of Langmuir’s model in the present system indicates the formation of monolayer coverage of the adsorbate species at the outer surface of adsorbent. The data thus obtained may prove of vital use for designing and fabricating a treatment plant for tailing waste management enriched in manganese and zinc
See related topics and documents: Use of Wollastonite for Tailing Waste Management Enriched in Mn and Zn.pdf
2.6 Wollastonite for toxic chromium removal
Abstract: Scientists at the Banaras Hindu University (BHU), India, have found that wollastonite is an efficient and economically viable material for the removal of toxic hexavalent chromium (Cr6+) from industrial wastewater effluents. Led by Dr Jogesh Sharma and funded by the Indian government, the project has now reached completion and the team at BHU are looking for potential industries that could implement wollastonite remediation systems in their operations and provide further funding for follow-up studies.
See related topics and documents: Wollastonite for toxic chromium removal.pdf
3. Carbon Sequestration
3.1 Fight Global Warming By Boosting Calcium Silicates In Soil – Theory
Plants, crops and trees naturally absorb atmospheric carbon dioxide (CO2) during photosynthesis and then pump surplus carbon through their roots into the earth around them. In most soils, this carbon can escape back to the atmosphere or enters groundwater.Knowing this, a team from Newcastle University aims to design soils that can remove carbon from the atmosphere, permanently and cost-effectively using soils containing calcium-bearing silicates.Calcium silicates are minerals that occur naturally in many different rocks and also in artificial materials such as concrete. (Wollastonite is a pure calcium silicate)The team believe the carbon that oozes out of a plant’s roots may react with the calcium to form the harmless mineral calcium carbonate(1). The carbon then stays securely locked in the calcium carbonate, which simply remains in the soil, close to the plant’s roots, in the form of a coating on pebbles or as grains.
See related topics and documents: Fight Global Warming By Boosting Calcium Silicates In Soil – Theory.pdf
3.2 Disposing Of Greenhouse Gases Through Mineralization Using The Wollastonite Deposits Of New York State
Abstract: This project explores the potential for mineral sequestration of carbon dioxide (CO2) in a carbonation reactor using wollastonite, a calcium silicate mineral found in large quantities in New York State. The project team will attempt to determine the optimum conditions for CO2 mineralization, including an assessment of the potential use of chemical additives. The results will be used to design multi-phase reactors to be employed for each stage of the process. The overall mass and energy balance of the process will be calculated, and mineral production and reserve data will be analyzed to estimate the carbon mineral sequestration capacity for New York State.
Findings: Wollastonite samples procured for this project were mostly mining tailings with a large particle size distribution. To obtain a uniform particle size for the kinetic studies, wollastonite samples were ground and separated by size. The average particle size for the fine wollastonite sample was 51.2 micrometers (μm). The particle density of the wollastonite sample was found to be 2.68 grams per millilitre (g/ml). Current project tasks include continuing the characterization and dissolution studies of the wollastonite samples and developing an efficient carbonation process.
See related topics and documents: Disposing of Greenhouse Gases through Mineralization – Update.pdf
3.3 Viability of Storage Options of CO2 in Ca Silicates
This report investigates a direct aqueous route of mineral carbonation of wollastonite under elevated pressure and temperature. Choice of the wollastonite was made based on its high reactivity rate and the method was determined by a catalytic effect of water on the adsorption kinetics. To improve the process and limit duration of the step where CO2 diffuses in solution before attaining the solid surface, most of the experiments were dedicated to carry in a moistened sample. As a result it could benefit from the catalytic effect of water and transport of CO2 was fast enough due to pressure equilibration. To investigate the influence of the water content of the sample, the experiments for this research were carried out with different water fractions.
See related topics and documents: MSc_Thesis_Report_AE_Peksa.pdf
3.4 Mechanisms Of Aqueous Wollastonite Carbonation As A Possible C02 Sequestration Process
Abstract: The mechanisms of aqueous wollastonite carbonation as a possible carbon dioxide sequestration process were investigated experimentally by systematic variation of the reaction temperature, C02 pressure, particle size, reaction time, liquid to solid ratio and agitation power. The carbonation reaction was observed to occur via the aqueous phase in two steps: (I) Ca leaching from the CaSi03 matrix and (2) CaC03 nucleation and growth. Leaching is hindered by a Ca-depleted silicate rim resulting from incongruent Ca-dissolution. Two temperature regimes were identified in the overall carbonation process. At temperatures below an optimum reaction temperature, the overall reaction rate is probably limited by the leaching rate of Ca. At higher temperatures, nucleation and growth of calcium carbonate is probably limiting the conversion, due to a reduced (bi)carbonate activity. The mechanisms for the aqueous carbonation of wollastonite were shown to be similar to those reported previously for an industrial residue and a Mg-silicate. The carbonation of wollastonite proceeds rapidly relative to Mg-silicates, with a maximum conversion in 15 min of70% at 200 °C, 20 bar C0 2 partial pressure and a particle size of <38 Jl.ID. The obtained insight in the reaction mechanisms enables the energetic and economic assessment of C02 sequestration by wollastonite carbonation, which forms an essential next step in its further development.
Conclusions: The aqueous carbonation of wollastonite for mineral C0 2 sequestration occurs in two subsequent steps via the aqueous phase (i.e., Ca-leaching and CaC0 3 precipitation). A key process variable is the specific surface area of the wollastonite particles. The applied C0 2 pressure determines the optimum reaction temperature at which maximum conversion is reached. At temperatures below the optimum, the overall reaction rate is probably limited by the leaching of Ca from wollastonite into the water phase, which is suggested to be controlled by diffusion of Ca through a Ca depleted silicate rim formed by incongruent leaching. At higher temperatures, a reduction of the bi(carbonate) activity probably causes the nucleation and growth of calcium carbonate to limit the conversion. The aqueous carbonation mechanisms of wollastonite, olivine and steel slag were shown to be generally similar. Wollastonite carbonates rapidly compared to Mg silicates, with a maximum convers ion in 15 min of 70% at relatively mild conditions (d<38 )liD, T = 200 °C and pc02 = 20 bar). However, resources of wollastonite are limited, relative to those of Mg-silicates. The process conditions required to sequester C02 by the aqueous carbonation of wollastonite seem technically feasible. However, the energy consumption and costs associated particularly with the grinding to a small particle size (e.g. <38 )liD or D[3,2] = 8 )llTI) are likely to be substantial. Therefore, an essential step in the further development of this process is an assessment of the energetic and economic feasibility of aqueous wollastonite carbonation as a possible C0 2 sequestration process.
See related topics and documents: Mechanisms of aqueous wollastonite carbonation as a possible CO2 sequestratin process.pdf
3.5 Aqueous Mineral Carbonation As A Possible CO2 Sequestration
Process: Energetic Efficiency And Costs Abstract: Aqueous mineral carbonation is a potentially attractive sequestration technology to reduce CO¬2 emissions. In this paper, the energy consumption and costs of this technology were assessed using either wollastonite (CaSiO3) or steel slag as feedstock. The major energy-consuming process steps were found to be the grinding of the feedstock and the compression of the CO2. Within ranges of experimentally investigated process conditions, optimum energetic CO2 sequestration efficiencies were 79 and 74% for wollastonite and steel slag, respectively. It was shown that the energetic performance for both feedstock might be improved up to >90% by e.g. further grinding of the feedstock and reducing the amount of process water applied. At energetically optimized process conditions, a preliminary cost estimate was made of 93 and 66 €/ton CO2 avoided for wollastonite and steel slag, respectively (sequestration costs excluding possible capture). For wollastonite, major costs were associated with the feedstock and the electricity consumption (51 and 20 €/ton CO2 avoided, respectively). A sensitivity analysis showed that additional influential parameters with regard to the sequestration costs include the liquid-to-solid ratio applied in the carbonation reactor and the possible commercial value of the carbonated product.
Conclusions: The presented system study of an aqueous mineral carbonation process has shown that the measures taken to increase the carbonation rate (i.e., grinding, heating and compression of CO2) were, in principle, energetically favourable. Within ranges of experimentally investigated carbonation conditions, the optimum energetic CO2 sequestration efficiencies were found to be 79 and 74% for wollastonite and steel slag, respectively. The sequestration efficiency can be further improved to >90% by e.g. further grinding of the feedstock and increasing the solid content in the carbonation reactor.
At energetically optimized process conditions, sequestration costs of 93 and 66 €/ton CO2 avoided were estimated for wollastonite and steel slag, respectively. State-of-the-art aqueous mineral carbonation seems a relatively expensive CO2 sequestration technology compared to both other CO2 storage technologies and (expected) CO2 market prices. Further research on cost reduction should focus on the major costs within the process (e.g., in the case of wollastonite, the feedstock and electricity consumed with 51 and 20 €/ton CO2 avoided, respectively). A sensitivity analysis showed that additional influential parameters on the sequestration costs include the liquid-to-solid ratio applied in the carbonation reactor and the possible commercial value of the carbonated product.
See related topics and documents: Aqueous Mineral Carbonation as a Possible CO2 Sequestration Process.pdf
3.6 Carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO(2)) at 50, 55 and 70 degrees C and 90, 120 and 160 bar.
Abstract: Reports from University of Central Missouri Advance Knowledge in Greenhouse Gas Control 2013 JUN 17 (VerticalNews) — By a News Reporter-Staff News Editor at Global Warming Focus — Researchers detail new data in Greenhouse Gas Control. According to news reporting from Warrensburg, Missouri, by VerticalNews journalists, research stated, “Subsurface injection of CO2 is commonplace in certain industries, yet deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability. Accurate modeling of subsurface geochemical processes related to geologic carbon sequestration requires experimentally derived data for mineral reactions.”
The news correspondents obtained a quote from the research from the University of Central Missouri, “Most work in this area has focused on aqueous-dominated systems in which dissolved CO2 reacts to form crystalline carbonate minerals. Comparatively little laboratory research has been conducted on reactions occurring between minerals in the host rock and the wet supercritical fluid phase. We studied the carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO(2)) at 50, 55 and 70 degrees C and 90, 120 and 160 bar. Reactions were followed by three novel in situ high pressure techniques, which demonstrated increased dissolved water concentrations in the scCO(2) resulted in increased wollastonite carbonation approaching similar to 50 wt.%. Overall, the X-ray diffraction and infrared and magic angle nuclear magnetic resonance spectroscopies experiments conducted in this study allow detailed examination of mechanisms impacting carbonation rates. These include the development of amorphous passivating layers, thin liquid water films, and amorphous hydrated carbonate phases.”
According to the news reporters, the research concluded: “Collectively, these results emphasize the importance of understanding geochemical processes occurring in wet scCO(2) fluids.”
For more information on this research see: Insights into silicate carbonation processes in water-bearing supercritical CO2 fluids – Abstract.pdf
3.7 Mineral Carbonation And Industrial Uses Of Carbon Dioxide
Executive summary: This Chapter describes two rather different options for carbon dioxide (CO2) storage: (i) the fixation of CO2 in the form of inorganic carbonates, also known as ‘mineral carbonation’ or ‘mineral sequestration’, and (ii) the industrial utilization of CO2 as a technical fluid or as feedstock for carbon containing chemicals.
In the case of mineral carbonation (see Section 7.2), captured CO2 is reacted with metal-oxide bearing materials, thus forming the corresponding carbonates and a solid byproduct, silica for example. Natural silicate minerals can be used in artificial processes that mimic natural weathering phenomena, but also alkaline industrial wastes can be considered. The products of mineral carbonation are naturally occurring stable solids that would provide storage capacity on a geological time scale. Moreover, magnesium and calcium silicate deposits are sufficient to fix the CO2 that could be produced from the combustion of all fossil fuels resources. To fix a tonne of CO2 requires about 1.6 to 3.7 tonnes of rock. From a thermodynamic viewpoint, inorganic carbonates represent a lower energy state than CO2; hence the carbonation reaction is exothermic and can theoretically yield energy. However, the kinetics of natural mineral carbonation is slow; hence all currently implemented processes require energy intensive preparation of the solid reactants to achieve affordable conversion rates and/or additives that must be regenerated and recycled using external energy sources. The resulting carbonated solids must be stored at an environmentally suitable location. The technology is still in the development stage and is not yet ready for implementation. The best case studied so far is the wet carbonation of the natural silicate olivine, which costs between 50 and 100 US$/tCO2 stored and translates into a 30-50% energy penalty on the original power plant. When accounting for the 10-40% energy penalty in the capture plant as well, a full CCS system with mineral carbonation would need 60-180% more energy than a power plant with equivalent output without CCS.
The industrial use of CO2 (see Section 7.3) as a gas or a liquid or as feedstock for the production of chemicals could contribute to keeping captured CO2 out of the atmosphere by storing it in anthropogenic carbon products. Industrial uses provide a carbon sink, as long as the pool size keeps growing and the lifetime of the compounds produced is long. Neither prerequisite is fulfilled in practice, since the scale of CO2 utilization is small compared to anthropogenic CO2 emissions, and the lifetime of the chemicals produced is too short with respect to the scale of interest in CO2 storage. Therefore, the contribution of industrial uses of captured CO2 to the mitigation of climate change is expected to be small.
See related topics and documents: Mineral carbonation and industrial uses of CO2.pdf
3.8 Emission Reduction Of Greenhouse Gases From The Cement Industry
Abstract: 5% of global carbon dioxide emissions originates from cement production. About half of it from calcination and half of combustion processes. A wide range of options exists to reduce CO2 emissions considerably.
Conclusions: In 1994 cement industry consumed 6.6 % of primary energy, corresponding with 2% of world energy consumption. Worldwide 1126 Tg CO2 or 5% of the CO2 production originates from cement production. The carbon intensity of cement making amounts to 0.81 kg CO2/kg cement. In India, North America, and China the carbon intensity is about 10% higher than on average. Specific carbon emissions range from 0.36 kg to 1.09 kg CO2/kg cement mainly depending on type of process, clinker/cement ratio and fuel used. On average a little above 50% of the emissions originates from the calcination step.
To reduce the carbon intensity the following options are identified: improving energy efficiency, shifting to more energy efficient process, shifting to lower carbon fuels, shifting to lower clinker/cement ratio, shifting to mineral polymers and removal of CO2.
Seventeen different energy efficiency improvement options are identified. The improvement ranges from a small percentage to more than 25% per option, depending on the reference case (i.e type of process, fuel used) and local situation. The use of waste instead of fossil fuel may reduce CO2 emissions by 0.1 to 0.5 kg/kg cement (varying from 20 to 40%). On average blended cements may reduce carbon emissions from 0.81 kg to 0.64 kg per kg cement (20%). Global potential of blended cements reducing carbon emissions is at least 5% but it is estimated to be as high as 20%. An end-of-pipe technology to reduce carbon emissions may be CO2 removal. Probably the main technique is combustion under oxygen while recycling CO2. However, considerably research is required to all unknown aspects of this technique.
See related topics and documents: Emission Reduction of Greenhouse Gasses from the Cement Industry.pdf
4. Stream Rehabilitation
4.1 Calcium Silicate Neutralizes An Acidic Stream
Abstract: As a remedy for acid stomach, people reach for Tums, or a similar calcium-based acid reducer. When attempting to increase pH-levels in acidic streams, scientists have historically used various forms of limestone, a natural source of calcium carbonate. Its neutralizing effects are short-lived, however, and can generate extreme fluctuations in water chemistry. Recognizing the limitations of limestone, Likens and colleagues looked to another material to neutralize an acidified stream at Hubbard Brook– Wollastonite.
Over one hundred and thirty pounds (61kg) of this naturally occurring calcium silicate mineral, mined from the Adirondacks and manufactured into a pellet form, was manually applied to the study stream. Pellets were added to 50-meters of the 910-meter stream, including the stream channel and adjacent stream bank. Researchers took extensive measurements of water attributes, such as pH and acid neutralizing capacity, before, during and after the application.
Despite the small treatment area, the buffering effects of the Wollastonite were long lasting. By adding the pellets to 5.5% of the stream, acidity was suppressed for over four months. It is likely that a larger addition would have resulted in a longer neutralizing effect. Wollastonite degraded slowly in the system; as a result water chemistry fluctuations were smaller than seen during lime additions.
See related topics and documents: Calcium Silicate Neutralizes An Acidic Stream.pdf
4.2 Effects Of A Whole-Watershed Calcium (Wollastonite) Addition On The Chemistry Of Stream Storm Events At The Hubbard Brook Experimental Forest In NH, USA
Abstract: Patterns of storm runoff chemistry from a wollastonite (calcium-silicate mineral, CaSiO3) treated watershed (W1) were compared with a reference watershed (W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire (NH), USA to investigate the role of Ca2+ supply in the acid–base status of stream chemistry. In the summer of 2003, six storm events were studied in W1 and W6 to evaluate the effects of the wollastonite treatment on the episodic acidification of stream waters. Although mean values of Ca2+ concentrations decreased slightly from 33.8 to 31.7 μmol/L with increasing stream discharge in W1 during the events, the mean value of acid neutralizing capacity (ANC) was positive (1.2 μeq/L) during storm events, compared to negative values (−0.2 μeq/L) in W6. This pattern is presumably due to enhanced Ca2+ supply in W1 (20.7 to 29.0% of dissolved Ca2+ derived from the added wollastonite) to stream water as a result of interflow along shallow flowpaths. In addition, the application of wollastonite increased pH and dissolved silica (H4SiO4) concentrations, and decreased the concentration of inorganic monomeric Al (Ali) in W1 in comparison with W6 during storm events. Despite an increase in SO4 2− concentration, likely due to desorption of sulfate from soil after the treatment, the watershed showed an increase in ANC compared to the reference watershed, serving to mitigate episodic acidification.
Conclusions: The variability in the hydro-biogeochemical interactions between a Ca-treated watershed (W1) and a reference watershed (W6) at the HBEF were examined during six storm events. Detailed analyses of the response of individual chemical species during storm episodes helped elucidate factors that control storm event chemistry. The Ca2+ concentrationswere higher in streamwater of W1, which was treated by wollastonite in 1999, resulting in higher pH and ANC and lower Ali concentrations compared to the reference watershed (W6). Historical acidic deposition has depleted pools of exchangeable Ca2+ in the forest floor, making acidification of surface waters more severe during episodes. However, stream water draining W1 had either no decrease or only slight dilution in Ca2+ concentrations compared to pre-event water and still exhibited a positive mean ANC value (1.2 μeq/L) even during storm events, in comparison with stream water draining W6. This phenomenon probably resulted from the transmission of water through organic horizon with elevated Ca2+ in soil water. This shift in hydrologic flowpath supplied available Ca2+ derived from wollastonite dissolution in this horizon into the stream channel. The enhanced supply of Ca2+ was a major factor increasing ANC during storm events compared to other cations and anions. The difference between pre-event ANC and the minimum ANC was also calculated for each storm event. The changes of ANC were 0.0 and −9.9 μeq/L during the large event, and −0.7 and −4.4 μeq/L during the small event at W1 and W6, respectively. Although the differences in pH, ANC, and Ali between W1 and W6 were relatively small following the wollastonite treatment, Ca and H4SiO4 concentrations were significantly greater in the treated watershed. This treatment bolstered stream Ca2+ concentrations and therefore limited the intensity of episodic acidification in summer storms in comparison with the reference watershed. We anticipate changes in biological structure and function associated with the watershed treatment which might include increases in stream microbial activity and macroinvertebrate diversity and production in the stream ecosystem due to the increase in pH and the decrease in Al.
4.3 Decreased water flowing from a forest amended with calcium silicate (Wollastonite)
Acid deposition during the 20th century caused widespread depletion of available soil calcium (Ca) throughout much of the industrialized world. To better understand how forest ecosystems respond to changes in a component of acidification stress, an 11.8-ha watershed was amended with wollastonite, a calcium silicate mineral, to restore available soil Ca to preindustrial levels through natural weathering. An unexpected outcome of the Ca amendment was a change in watershed hydrology; annual evapotranspiration increased by 25%, 18%, and 19%, respectively, for the 3 y following treatment before returning to pretreatment levels. During this period, the watershed retained Ca from the wollastonite, indicating a watershed-scale fertilization effect on transpiration. That response is unique in being a measured manipulation of watershed runoff attributable to fertilization, a response of similar magnitude to effects of deforestation. Our results suggest that past and future changes in available soil Ca concentrations have important and previously unrecognized implications for the water cycle.
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