Pol Knops - Academia.edu (original) (raw)

Papers by Pol Knops

AGU Fall Meeting Abstracts, Dec 1, 2018

AGU Fall Meeting Abstracts, Dec 11, 2019

Minerals

Olivine, one of the most abundant silicates on earth, thermodynamically captures CO2 in relevant ... more Olivine, one of the most abundant silicates on earth, thermodynamically captures CO2 in relevant amounts during its dissolution. Upscaling the use of this mineral as a replacement for sand or gravel may contribute to reduce concentrations of greenhouse gasses in the atmosphere. However, the reliable quantification of weathering rates and prognoses for effects of various environmental conditions on weathering are lacking. This currently inhibits the monitoring, reporting and verification of CO2 capture and hampers the exploitation of the carbon dioxide removal economy. A mineral dissolution model was developed, and olivine weathering rates were directly coupled to particle sizes of the ground mineral. A particle size-dependent calculation approach, based on the shrinking core model, showed faster weathering rates as compared to a single-size, monodisperse approach. This provided a better underpinning of the prediction of the overall weathering and, consequently, the sequestration rat...

AGU Fall Meeting Abstracts, Dec 1, 2020

In this work, we explore a novel mineral processing approach using carbon dioxide to promote mine... more In this work, we explore a novel mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4). The precept is that by altering the morphology and the mineralogy of the ore via mineral carbonation, the comminution requirements and the acid consumption during hydrometallurgical processing can be reduced. Furthermore, carbonation pre-treatment can lead to mineral liberation and concentration of metals in physically separable phases. In a first processing step, olivine is fully carbonated at high CO2 partial pressures (35 bar) and optimal temperature (200 °C) with the addition of pH buffering agents. This leads to a powdery product containing high carbonate content. The main products of the carbonation

Metals, 2020

This work continues on from previous studies showing that mineral sequestration by carbonation of... more This work continues on from previous studies showing that mineral sequestration by carbonation of magnesium or calcium silicates under high pressure and high temperature can be successfully carried out by processing in an autoclave. The paper is focused on the influence of experimental parameters on avoiding scale formation during pre-treatment in an autoclave and a subsequent leaching. Amorphous silica and magnesite, respectively, were the main reaction products in a carbonation of olivine under high pressure conditions in an autoclave. In addition, the examined peridotites may be accompanied by small to medium amounts of nickel or other metals, the recovery of which will be investigated in the present study: Extraction of metals such as nickel, iron, and magnesium from olivine bearing ore using hydrochloric acid under atmospheric pressure was studied between 50 and 90 °C in 1 h. The obtained results have shown maximal leaching efficiency of about 35% for Ni, Fe, and Mg under atmos...

Metals, 2019

Silicon dioxide nanoparticles, also known as silica nanoparticles or nanosilica, are the basis fo... more Silicon dioxide nanoparticles, also known as silica nanoparticles or nanosilica, are the basis for a great deal of biomedical and catalytic research due to their stability, low toxicity and ability to be functionalized with a range of molecules and polymers. A novel synthesis route is based on CO2 absorption/sequestration in an autoclave by forsterite (Mg2SiO4), which is part of the mineral group of olivines. Therefore, it is a feasible and safe method to bind carbon dioxide in carbonate compounds such as magnesite forming at the same time as the spherical particles of silica. Indifference to traditional methods of synthesis of nanosilica such as sol gel, ultrasonic spray pyrolysis method and hydrothermal synthesis using some acids and alkaline solutions, this synthesis method takes place in water solution at 175 °C and above 100 bar. Our first experiments have studied the influence of some additives such as sodium bicarbonate, oxalic acid and ascorbic acid, solid/liquid ratio and p...

Metals, 2018

Magnesium carbonate powders are essential in the manufacture of basic refractories capable of wit... more Magnesium carbonate powders are essential in the manufacture of basic refractories capable of withstanding extremely high temperatures and for special types of cement and powders used in the paper, rubber, and pharmaceutical industries. A novel synthesis route is based on CO2 absorption/sequestration by minerals. This combines the global challenge of climate change with materials development. Carbon dioxide has the fourth highest composition in earth’s atmosphere next to nitrogen, oxygen and argon and plays a big role in global warming due to the greenhouse effect. Because of the significant increase of CO2 emissions, mineral carbonation is a promising process in which carbon oxide reacts with materials with high metal oxide composition to form chemically stable and insoluble metal carbonate. The formed carbonate has long-term stability and does not influence the earth’s atmosphere. Therefore, it is a feasible and safe method to bind carbon dioxide in carbonate compounds such as mag...

Environmental science & technology, Jan 20, 2017

Enhanced weathering of (ultra)basic silicate rocks such as olivine-rich dunite has been proposed ... more Enhanced weathering of (ultra)basic silicate rocks such as olivine-rich dunite has been proposed as a large-scale climate engineering approach. When implemented in coastal environments, olivine weathering is expected to increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marine olivine weathering and its effect on seawater-carbonate chemistry remain poorly understood. Here, we present results from batch reaction experiments, in which forsteritic olivine was subjected to rotational agitation in different seawater media for periods of days to months. Olivine dissolution caused a significant increase in alkalinity of the seawater with a consequent DIC increase due to CO2 invasion, thus confirming viability of the basic concept of enhanced silicate weathering. However, our experiments also identified several important challenges with respect to the detailed quantification of the CO2 sequestration efficiency under field co...

Frontiers in Energy Research, 2016

To overcome the challenges of mineral CO2 sequestration, Innovation Concepts B.V. is developing a... more To overcome the challenges of mineral CO2 sequestration, Innovation Concepts B.V. is developing a unique proprietary gravity pressure vessel (GPV) reactor technology and has focussed on generating reaction products of high economic value. The GPV provides intense process conditions through hydrostatic pressurization and heat exchange integration that harvests exothermic reaction energy, thereby reducing energy demand of conventional reactor designs, in addition to offering other benefits. In this paper, a perspective on the status of this technology and outlook for the future is provided. To date, laboratory-scale tests of the envisioned process have been performed in a tubular "rocking autoclave" reactor. The mineral of choice has been olivine [~Mg1.6Fe 2+ 0.4(SiO4) + ppm Ni/Cr], although asbestos, steel slags, and oil shale residues are also under investigation. The effect of several process parameters on reaction extent and product properties has been tested: CO2 pressure, temperature, residence time, additives (buffers, lixiviants, chelators, oxidizers), solids loading, and mixing rate. The products (carbonates, amorphous silica, and chromite) have been physically separated (based on size, density, and magnetic properties), characterized (for chemistry, mineralogy, and morphology), and tested in intended applications (as pozzolanic carbon-negative building material). Economically, it is found that product value is the main driver for mineral carbonation, rather than, or in addition to, the sequestered CO2. The approach of using a GPV and focusing on valuable reaction products could thus make CO2 mineralization a feasible and sustainable industrial process.

Metals, 2015

Chemical Engineering Science, 2017

Industrial olivine has been carbonated at 175°C, 100 bars in a mixture of supercritical CO 2 and ... more Industrial olivine has been carbonated at 175°C, 100 bars in a mixture of supercritical CO 2 and an aqueous solution, for 30 min to 12 hours in a rocking batch autoclave. Simple settling of the solids recovered after the reaction led to a "fines" fraction and a coarser (residue) fraction. The carbonation extent of olivine was limited to 30 % mainly because of the size of the olivine particles used, centered at 138 µm. Observation and characterization of the solids showed that the residue is principally formed by unreacted olivine, whereas the fines consist mainly of carbonates (below 40 µm) with more silica in the range 40-106 µm: this segregation with particle size appears promising for separated beneficiation of the silica and the carbonates formed.

ABSTRACT A multitude of chemical reactions rely on high temperatures and pressures to attain suit... more ABSTRACT A multitude of chemical reactions rely on high temperatures and pressures to attain suitable kinetics and reach desirable conversions, which are commonly delivered in autoclave reactors. Traditional reactor designs (e.g. CSTRs) have large energy demands (due to pressurization and mixing demands, and heat losses) and costly construction specifications (to meet pressurized vessel codes and safety provisions), which make certain processing routes prohibitively expensive. An alternative reactor technology, which cleverly applies the principles of process integration and process intensification [1], is the Gravity Pressure Vessel (GPV). This is a special kind of autoclave with a built-in heat exchanger, plug flow configuration, and gravity driven pressurization/depressurization. Residence time is controlled by the reactor length that can reach up to 2400 m, resulting in hydrostatically built pressures that can exceed 120 bar. By continuously recycling exothermic reaction heat, up to 70% of the energy can be conserved, and high end temperatures can be achieved (up to 500 °C). In the case of slurry flow, the generated turbulence promotes particle-particle interaction, removing passivating layers and autogenously milling the reacting material, permitting post-processing separation of the mineral phases into valuable product streams. The first patent of the GPV technique was granted in 1981 (US4272383) for wet-air oxidation of sewage sludge. This process was in operation for 12 years in Apeldoorn (the Netherlands), reducing chemical oxygen demand (COD) by &gt;70% and generating up to 10 MW in heat output. Recently, Innovation Concepts B.V. patented the ‘CO2 Energy Reactor™’ (WO2011/155830A1), an application of GPV to mineral carbonation. This is an economically viable, socially acceptable and environmentally sustainable process that permanently sequesters CO2; an alternative to underground storage. It utilizes alkaline minerals (virgin or waste-derived), rich in calcium (e.g. wollastonite, steel slags and incineration ashes) or magnesium (e.g. olivine, serpentine, asbestos and mine tailings) as carbon sinks. Besides carbon capture, valuable product streams also emerge: precipitated carbonates, amorphous silica, and enriched metal residues. This solution results in the stabilization or detoxification of hazardous industrial wastes, and in the valorisation of abundant low-value minerals. The GPV technology is also being developed for the oil sands industry. Bituminous sands are a type of unconventional petroleum deposit consisting of a mixture of sand, clay, water, and a dense and extremely viscous form of petroleum (the bitumen or “tar”). GPV technology is a sustainable solution to one main problem area: oil sand tailings treatment. Wet-air oxidation permits the conversion of MFT (Mature Fine Tailings) to TTT (Thermally Treaded Tailings), wherein residual bitumen in MFT is used as energy source for the process. The outcome is reduced settling time, metals oxidation, reduced contaminants leaching, and freed water that can be re-used in the separation process. This work reports on the technical aspects of the GPV technology, and on the latest developments, challenges and outlook for its adaptation to the considered applications and adoption by the mainstream industry. [1] Santos, R.M., Van Gerven, T. (2011) Process intensification routes for mineral carbonation. Greenhouse Gases: Science and Technology 1(4), 287–293.

To overcome the limitations of mineral carbonation that thus far have prevented it from becoming ... more To overcome the limitations of mineral carbonation that thus far have prevented it from becoming an acceptable route to sustainable CO2 sequestration, a novel reactor technology that makes use of a Gravity Pressure Vessel is 2 cess integration and process intensification to achieve the technological leap needed to make mineral carbonation industrially feasible. Its autothermicity, hydrostatic pressurization, vertical plug flow design and underground installation make it an appealing alternative to other CCS techniques. This work reports the technical details of the conceptual design, and studies the effect of process parameters on reaction characteristics (kinetics and conversion) and energy balances by means of mathematical modeling. The parameter sets (particle size, solids loading, pumping rate, and reactor dimensions) that ensure autothermic behavior, maximize carbonation efficiency and enable recoverable heat generation are identified.

ABSTRACT In this work, we explore a novel mineral processing approach using carbon dioxide to pro... more ABSTRACT In this work, we explore a novel mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4). The precept is that by altering the morphology and the mineralogy of the ore via mineral carbonation, the comminution requirements and the acid consumption during hydrometallurgical processing can be reduced. Furthermore, carbonation pre-treatment can lead to mineral liberation and concentration of metals in physically separable phases. In a first processing step, olivine is fully carbonated at high CO2 partial pressures (35 bar) and optimal temperature (200 °C) with the addition of pH buffering agents. This leads to a powdery product containing high carbonate content. The main products of the carbonation reaction include amorphous colloidal silica, chromium-rich metallic particles, and iron-substituted magnesite ((Mg1-x,Fex)CO3). Carbonated olivine was subsequently leached using an array of inorganic and organic acids to test their leaching efficiency. Compared to leaching from untreated olivine, the percentage of nickel extracted from carbonated olivine by acid leaching was significantly increased. It is anticipated that the mineral carbonation pre-treatment approach may also be applicable to other ultrabasic and lateritic ores.

Because of the significant increase of CO2 emissions, mineral carbonation is a promising process ... more Because of the significant increase of CO2 emissions, mineral carbonation is a promising process in which carbon oxide reacts with materials containing high metal oxide composition such as magnesium oxide, calcium oxide and iron oxide to form metal carbonate. The formed carbonate has long-term stability and does not influence the earth’s atmosphere. The subject of this work is the carbonation of an olivine (Mg2SiO4) from Norway and reference magnesia material under high pressure and temperature in an autoclave. First experiments have confirmed the positive influence of additives such as sodium bicarbonate, oxalic acid and ascorbic acid on the carbonation efficiency. The maximal carbonation efficiency was amounted 79.86 % for NedMag99 reference sample in an autoclave (T = 175 °C, 1 L, 117 bar CO2, 600 rpm, 2 hours) in the presence of additives of sodium carbonate, oxalic and ascorbic acid. Under same conditions the carbonation efficiency of the Steinsvik olivine was 44.56 %.