Aluminum silicate scale formation and inhibition (2): scale solubilities and laboratory and field inhibition tests

The solubilities of pure silica, iron-silicate and aluminum-silicate scales were measured in water from 25–250°C in a laboratory pressure reactor. Iron- and aluminum-silicate scales are significantly less soluble than pure amorphous silica. Aluminum- and iron-rich silica scales at equilibrium conditions are predicted to deposit from near-neutral, low salinity brines at temperatures that are 25 and 75°C above the saturation point for pure amorphous silica, respectively. This laboratory study demonstrates that higher brine injection temperatures are required to mitigate aluminum- and iron-rich silica scaling compared with pure amorphous silica. In a laboratory scale test, pure amorphous silica and aluminum-rich silica deposition rates have been measured at high degrees of supersaturation in the presence of potential inhibitors. Scale deposition was best inhibited by brine pH modification techniques. A commercially available dispersant successfully inhibited amorphous silica scaling, but exacerbated aluminum silicate scaling. Scale inhibition was also achieved in the presence of aluminum complexing\sequestering agents in a patent-pending process. Screening of these potential silica- and aluminum-silicate scale inhibitors in the laboratory will focus the efforts of ongoing field pilot scale testing. The effect of complexing\sequestering agents on scale inhibition was monitored in preliminary field pilot tests. These complexing agents achieved 25% to 80% aluminum silicate scale inhibition.     

The use of reducing agents for control of ferric silicate scale deposition

A process has been developed to inhibit the deposition of ferric silicate scales from high-temperature, hypersaline geothermal brines, such as those encountered at the Salton Sea, California, geothermal field. Scale control is achieved by injecting sufficient reducing agent into the brine to effectively reduce trivalent iron to the divalent state. Scale deposition is decreased as a result of ferrous silicate being more soluble in these brines than ferric silicate. Furthermore, scaling can also be controlled by simultaneously blending into the brine a reducing agent and a small amount of acid sufficient to decrease the pH of the brine by up to 0.5 units. The use of reducing agents to control ferric silicate scale has also proven to mitigate corrosion of brine-handling equipment.     

Chemistry of silica in Cerro Prieto brines

We have studied the precipitation of amorphous silica from synthetic geothermal brines that resemble the flashed brine at Cerro Prieto. We found that part of the dissolved silica quickly polymerizes to form suspended colloidal silica. The colloidal silica flocculates and settles slowly at unmodified brine pH values near 7.35. Raising the pH of the brine to about 7.8 by adding base and stirring for a few minutes causes rapid and complete flocculation and settling. These results have been confirmed in the field using actual Cerro Prieto brine. Several commercially available flocculating agents were also tested. Both in the laboratory and in the field, we found quaternary amines to be effective with some brine compositions but not with others.These results suggest the following simple preinjection brine treatment process: age the brine for 10 – 20 min in a covered holding tank, add 30 to 40 ppm lime (Ca(OH)₂), stir for 5 min, and separate the flocculated silica from the brine using a conventional clarifier. The brine coming out of such a process will be almost completely free of suspended solids.The pilot plant tests needed to reduce this conceptual process to practice are discussed.In a separate study, we researched the rate of deposition of silica scale from synthetic brines. We found that a modest decrease in pH could significantly reduce the scaling rate at a reasonable cost.     

Reactive transport modeling of injection well scaling and acidizing at Tiwi field,Philippines

Hot brine injector Nag-67 in the Tiwi geothermal field (Philippines) had been in operation for over 10 years when injectivity decline indicated a workover was required in 2000. The operation consisted of drilling-out wellbore scale followed by acid dissolution of scale formed in the near-wellbore formation. The workover increased the injection capacity of the well to near its initial-use capacity. Scale-volume estimates from brine chemistry, and from stoichiometric amounts of silica dissolved during the acidizing, suggested that the decrease in injectivity was largely due to scale deposition in the near-well formation. Reactive transport modeling was used to simulate mineral deposition and injectivity loss. A porosity–permeability relationship was calibrated using observed injection indexes to reproduce the loss of injectivity. The relationship captured very well the steep loss of injectivity, and the simulated amounts of precipitated amorphous silica were consistent with the estimated amounts from field data. Significant precipitation of amorphous silica, and reductions in porosity and permeability, were predicted to occur mainly within a 10 m radius from the well. Injectivity recovery by acid injection was also simulated, and the predicted amount of amorphous silica dissolved by acid was consistent with the estimated amount.     

Silica removal from Mokai, New Zealand, geothermal brine by treatment with lime and a cationic precipitant

Preliminary experiments using two chemicals (CaO, a quicklime, and a cationic nitrogen-bearing precipitant, EC-004) to remove silica from geothermal brine were undertaken at the Mokai geothermal plant, New Zealand. The brine was mixed with the reagent (CaO or EC-004). The reaction was studied from the start of the experiment (NRT, 0 min, no retaining time) and after 15 min (15RT) at 90 °C. The concentration of silica in the brine was initially 954 mg/l, and decreased linearly with increasing reagent concentration. When CaO is added, the silica concentration at 15RT was 200 mg/l lower than at NRT and became almost zero on addition of 1.5 g/l. In contrast, when EC-004 is added, the total silica concentration nearly reaches the solubility of amorphous silica at 90 °C. In order to prevent silica scaling in Mokai brines cooled to 90 °C, the CaO and EC-004 added should be individually adjusted to 0.5 g/l and 80 mg/l, respectively.     

pH and silica scaling control in geothermal field development

Due to the increase of amorphous silica solubility as significant silicate ion forms in the pH range 7 to 8.5, the potential for the deposition of silica scale during reticulation (pipeline transmission) of waste geothermal waters to disposal sites is dependent on steam separation temperature, silica concentration and the pH of the residual fluid. For low salinity geothermal fluids the latter is related to the composition of the fluid, particularly the concentration of carbon dioxide remaining after the removal of steam for power generation using conventional separators. In general terms the higher the gas content of the initial deep aquifer fluid, the higher will be the pH of the waste waters, so that in many fields, where reservoir temperatures fall in the range 250 to 280°C, careful choice of separation pressures to maximise gas removal and hence elevate the pH of residual waters may obviate the problems of silica deposition, or the need to install costly chemical treatments such as acid or alkali addition. In designing and operating separators or flash plants it is important to avoid carryover of steam (containing CO₂ and H₂S) into the water reticulation lines, where, after heat loss, condensation occurs with resultant lower pH and higher scaling potential. Where flash plants are designed to receive a mixture of the two-phase discharges from a number of wells, consideration of the pH of the residual water resulting from steam separation may provide design constraints on the reticulation network such that silica scaling potential is minimised or entirely avoided. The Wairakei and Broadlands (Ohaaki) fields are used as examples of these design considerations in relation to the reservoir chemistry of the field and possible changes during extensive exploitation.     

地热流体开发利用中防垢除垢技术研究进展

地热流体结垢是阻碍地热资源稳定、经济和高效开发利用的因素之一。系统总结了中高温地热流体开发利用中防垢除垢技术研究进展。中高温地热田中代表性垢物是钙垢和硅垢,其中钙垢成分以CaCO₃为主,多形成于因压力下降导致CO₂脱气的开采井或者地面设备,硅垢成分以无定型SiO₂为主,多形成于因温度下降导致的溶解度减小的回灌井或者地面设备。实际生产中防垢除垢技术应结合地热流体利用方式进行选择和优化,直接利用方式可考虑采用基于CaCO₃和无定型SiO₂热力学性质的防垢技术;发电方式中钙垢可考虑阻垢剂注入的防垢技术,而硅垢则考虑利用石英和无定型SiO₂溶解度差异、调控温度、pH、无定型Si O₂浓度等防垢技术。     

Scale prevention method by brine acidification with biochemical reactors

Siliceous scale deposition often causes serious problems in geothermal power stations. In order to solve these problems, a number of scale prevention methods have been proposed to date, one of which is brine acidification. Although it is well known that silica deposition is prevented by keeping the pH of the geothermal brine acidic, the pH adjustment of the brine by mineral acid injection has not been commercially applied so far in geothermal power stations. A new method is proposed in which sulfuric acid can be biochemically manufactured from hydrogen sulfide in the gas exhausted from geothermal power stations. The applicability of this method has been experimentally confirmed in field tests with a biochemical reactor. It is believed that the method will provide an economical and environmentally-friendly acidification process to prevent siliceous scale deposition and will also contribute to the reduction of hazardous hydrogen sulfide emission from geothermal power stations.     

Impact of silica scaling on the efficiency of heat extraction from high-temperature geothermal fluids

In high-temperature geothermal fields, precipitation of amorphous silica from solution to form silica scales is the main obstacle to efficient heat extraction from the hot fluids. The silica deposits cause operational problems and may even clog pipelines and injection drillholes. The rate of silica-scale formation can be reduced by ageing amorphous silica super-saturated waters, thus allowing the aqueous silica in excess of saturation to polymerize. Polymeric silica shows less tendency to precipitate from solution than monomeric silica. Studies of separated water from the Nesjavellir geothermal power station, Iceland, indicate that silica-scale formation can be avoided during heat extraction by rapid cooling of the water in “capillary heat exchangers”, followed by ageing the water for 1–2 h and subsequently mixing it with condensed steam. It is thus possible to avoid scale formation during injection of the amorphous silica super-saturated water leaving the heat exchanger.     

Amorphous silica and its effects on shale reservoir: A case study about Yanchang formation lacustrine shale,Ordos Basin

The content of amorphous silica in Yanchang formation shale ranges from 1.48% to 19.89%, with an average of 11.77%. The Chang 7–3 submember (the submember 3 of the seventh member of Upper Triassic Yanchang formation) shale contains much larger content of amorphous silica. Amorphous silica appears as opal rim closely adjacent to detrital quartz, cement among clay minerals, and cement aside detrital minerals. Silica originates from clay mineral transformation and pressure solution of detrital quartz. Mineral composition, growth space, and overpressure affect the content of amorphous silica. Amorphous silica reduces the brittleness of shale reservoir, decreases the density of Chang 7–3 submember shale, and causes an increase in AC values for Chang 7–3 submember shale.     

Effect of silica polymerisation and pH on geothermal scaling

Siliceous scales were formed under controlled conditions from geothermal discharge waters, in contact with air, flowing over ceramic tiles and through steel pipes. Waters were aged for different periods, resulting in different degrees of polymerisation of silica. Ageing discharge waters from Broadlands and Wairakei (in New Zealand) was not an effective method for reducing the amount of scale formed; however the physical appearance of the scales could be changed by ageing.Water at normal pH (7·5–9) was also compared with water acidified to a pH of about 4. The acidified discharge water formed scales up to one hundred times slower than untreated water. It is suggested that acidification may be a practical method for minimising scale formation.     

Geochemical reactions-induced hydrogen loss during underground hydrogen storage in sandstone reservoirs

Underground hydrogen storage (UHS) appears to be an important means as a large-scale and long-term energy storage solution. A primary concern of UHS is the in-situ geochemical reactions-induced hydrogen loss. In this context, we performed geochemical modelling to examine the hydrogen loss associated with hydrogen dissolution and fluid-rock interactions using PHREEQC (Version 3) as a function of temperature and pressure. We also performed geochemical modelling with kinetics to investigate the potential hydrogen loss in two commercial gas storage reservoirs (Tubridgi and Mondarra) in Western Australia against the reservoir mineralogy, fluid properties, depth and temperature.Our results show that increasing pressure and temperature only slightly increases hydrogen solubility in brines without minerals. Increasing salinity slightly decreases the solubility of hydrogen in brines. The saturated hydrogen aqueous solution almost does not react with silicate and clay minerals, which is favorable for underground hydrogen storage in quartz-rich sandstone reservoirs. However, unlike silicate and clay minerals, carbonates like calcite triggers up to 9.5% hydrogen loss due to calcite dissolution induced hydrogen dissociation process. Kinetic simulations show that Tubridgi only leads to 0.72% of hydrogen loss, and Mondarra causes 2.76% of hydrogen loss as a result of reservoir calcite dissolution and hydrogen dissociation in brines in 30-year time. Nearly over 87% of calcite cement from Mondarra may be dissolved in 30-year, suggesting potential risks associated with wellbore stability. In conclusion, geochemical reactions-induced hydrogen loss would be minor for UHS in porous media, and we argue that deep calcite-free reservoirs together with calcite-free caprocks would be preferable for underground hydrogen storage.     

Purification of brines by chemical precipitation and ion‐exchange processes for obtaining battery‐grade lithium compounds

Lithium salts are very important in the production of lithium batteries since they are used as precursors for the fabrication of cathode materials that require very low level of impurities (battery grade). Usually, the lithium extraction process from brine first yields lithium carbonate, which is then used as raw material for the production of other lithium compounds. However, it implies an increase in investment costs, considering more equipment and process stages. To remove the impurities and produce battery‐grade lithium compounds directly from brines, a laboratory‐scale process was developed using the methods of ion exchange and chemical precipitation. Thus, impurity‐free brine ready to be used in an industrial membrane electrolysis process is obtained. Different sequences and operating conditions were investigated for the purification of lithium‐concentrated brines, removing the main impurities of the natural brines: calcium, magnesium, and sulfate. For the characterization of solutions, crystals, and ion‐exchange resins, atomic absorption spectrophotometry, scanning electron microscopy, and X‐ray scattering spectroscopy were used. The results indicate that during the chemical precipitation process, lithium‐concentrated brine reacted with some additives (precipitating agents) at different stages in the batch reactors. Subsequently, the pulp obtained was sedimented and filtered, eliminating or reducing the impurities of the lithium brine. Thus, the most efficient precipitation sequence was evaluated as a function of the removal percentage of the species. The removal efficiencies obtained for Ca⁺², Mg⁺², and SO₄^?2 were of 98.93%, 99.93%, and 97.14%, respectively. Thereafter, the use of the ion‐exchange resins reduced the concentration of Ca⁺² and Mg⁺² to the values below 1 ppm. The combined use of both processes provided promising results that could be applied in the industry.     

Investigations of organic inhibitors for silica scale control from geothermal brines–II

In an effort to find alternatives to brine acidification for control of siliceous scale deposition in geothermal resource production facilities, a second series of laboratory screening tests with new organic inhibitors has been conducted. In the first series of tests, organic inhibitors, usually consisting of dispersants and phosphino-carboxylic acid mixtures, were examined for silica scale control activity [Gallup, D.L., 2002. Investigations of organic inhibitors for silica scale control in geothermal brines. Geothermics 31, 415–430]. The present study consisted of screening additional inhibitor formulations obtained from seven different manufacturers in a laboratory pressure reactor using a synthetic brine solution. Several of the organic inhibitors yielded promising scale deposition results. Similar to the initial series of tests, brine acidification always out-performed the organic inhibitors. Acid precursors also appear to be acceptable alternatives to strong acids as a means of limiting corrosion, transportation risks and safety/handling issues.     

The aqueous chemistry of aluminum. A new approach to high-temperature solubility measurements

Predictions of changes in geothermal reservoir permeability and porosity during exploitation and reinjection, as well as aluminosilicate scale formation in wells and plant equipment, are currently limited by inaccuracies and discrepancies in our knowledge of the aqueous speciation of aluminum and the solubilities of aluminosilicates in high-temperature brines. To address this problem, the solubility of pure synthetic boehmite (AlOOH) has been measured in noncomplexing solutions over a wide range of pH (2–10), temperature (100–290°C), and ionic strength (0.03–1 mol·kg⁻¹ NaCl) in a hydrogen-electrode concentration cell (HECC) that provided continuous, in situ measurement of hydrogen ion molality. This represents the first such study ever reported of a pH-dependent mineral solubility profile across the entire pH range of natural waters at temperatures above 100°C.Samples of the solution were withdrawn after the pH reading stabilized for analysis of total aluminum content by ion chromatography. Acidic or basic titrants could then be metered into the cell to affect a change in the pH of the solution. The direction of approach to the equilibrium saturation state could be readily varied to ensure that the system was reversible thermodynamically. A least-squares regression of the results obtained at low ionic strength was used to determine the molal solubility products (Q_s0to Q_s4) of boehmite, which allowed comparison with those obtained from two recently-reported high-temperature studies of boehmite solubility, which relied on the conventional batch technique. Comparisons are also made with the low-temperature (<90°C) hydrolysis constants for aluminum obtained from solubility measurements with gibbsite as the stable phase. Based on these results, it is possible to draw some general conclusions concerning the relative importance of the aluminum species in solution and to reduce significantly the number of experiments needed to define this complex system. Finally, the application of this new technique to the study of the kinetics and thermodynamics of the dissolution and formation of more complex aluminosilicate minerals is discussed.     

Controlled silica precipitation in geothermal brine at the reykjanes geo-chemicals plant

This article describes how silica was precipitated in an electromagnetic field from silica supersaturated brine. At the Reykjanes Geo-Chemicals plant deposition of silica was a serious problem. After acidification of brine to pH 2.5 before evaporation the silica can be kept in solution for a considerable time. In order to precipitate silica out of this brine caustic soda is added. To get an effective precipitation of silica, a pH of at least 8.2 has to be reached. By using an electromagnetic field, a pH of 7.3–7.8 is sufficient to precipitate silica and an increased settling rate is observed. Settling rates were found to be from 7.1–9.7 cm/min at 100°C and from 3.4–4.6 cm/min at 40°C, compared to 1.3 cm/min for silica which was only alkalized. Higher effluent purity is also achieved by using electromagnetic field to precipitate out slilica.     

Desalination of geothermal brines by means of combustion residues?

Geothermal brines with high salinity are frequently encountered. Their commercial utilization, e.g. for heat recovery, is handicapped by scaling and disposal problems. A simple method for attaining a significant reduction of salinity would solve this problem. This paper examines the possibility of desalinating by entrapment of sodium chloride in sodalite. Sodalite is formed by the reaction of a hot brine with materials containing aluminum and silicon, e.g. combustion residues. We have reduced the sodium chloride content of a model brine in this manner.     

黏土矿物在电池领域的应用研究进展

黏土矿物是一类含水硅酸盐矿物,主要含铝、镁等元素,在我国储量丰富、价格低廉。基于其晶体结构、微观形态和物化特性,黏土矿物可用于制备电池材料,改善电池性能。本文简述了凹凸棒石(坡缕石)、海泡石、蒙脱石等黏土矿物在电池电解质、电极材料中的研究进展,对存在的问题进行了分析,为下一步的研究提出了建议。     

Chemical analyses of geothermal waters and strategic petroleum reserve brines for metals of economic importance

Waters from seven hydrothermal-geothermal, one geopressured-geothermal, and six Strategic Petroleum Reserve wells have been surveyed for 12 metals of economic importance using trace chemical analysis techniques. The elements sought were Cr, Co, Mn, Ta, Sn, V, Nb, Li, Sr, Pt, Au and Ag. Platinum was found at a concentration of 50 ppb in a brine from the Salton Sea geothermal area. Brine from this region, as has been known from previous studies, is also rich in Li, Sr and Mn. Higher concentrations (900 ppm) of Sr are found in the high-salinity geopressured brines. None of the fluids contained interesting concentrations of the other metals. Good recovery of precious metals at sub-ppm concentrations from synthetic high salinity brines was achieved using Amborane reductive resin, but similar recovery in the laboratory using real brines could not be demonstrated. Several analytical techniques were compared in sensitivity for the determination of the precious metals; neutron activation analysis with carrier separation is the best for gold and platinum in geothermal brines.     

An integrated technique using solar and evaporation ponds for effective brine disposal management

Desalination is a process that involves the removal of salts and non-ionic minerals from seawater to produce freshwater that is fit for human consumption. This process produces brine, which is typically redisposed into the sea. The relatively high salt concentration in the disposed brine increases the salinity of water and soil, which adversely affects the environment. However, brine is found to be rich in economically valuable minerals. In order to effectively manage the disposed brine, this study proposes an integrated technique using solar and evaporation ponds to filter valuable minerals from concentrated brine. The results of this study demonstrate that the proposed technique can be effectively employed for this purpose. Furthermore, this helps reduce desalination costs and complies with the notion of renewable energy production and eco-friendliness.