Minerals recovery from salton sea geothermal brines: a literature review and proposed cementation process

The potential for minerals recovery from a 1000-MWe combined geothermal power and minerals recovery plant in the Salton Sea is examined. While the possible value of minerals recovered would substantially exceed the revenue from power production, information is insufficient to carry out a detailed economic analysis. The recovery of precious metals—silver, gold and platinum—is the most important factor in determining the economics of a minerals recovery plant. However, the precious metal content of the brines is not certain. Such a power plant could recover 14–31% of the U.S. demand for manganese and substantial amounts of zinc and lead. Previous work on minerals extraction from Salton Sea brines is reviewed and a new process, based on a fluidized-bed cementation reaction with metallic iron, is proposed. This process would recover the precious metals, lead and tin present in the brines.     

Sodium/lithium ratio in water applied to geothermometry of geothermal reservoirs

We propose here a new geothermometer for natural waters. Analyses from many explored geothermal fields allow us to define two empirical thermometric relationships.One is for waters of low to moderate salinity (Cl⁻< 0·3 M) log Na/Li = 1000/T −0·38 and one for marine waters and brines (Cl⁻ > 0·3 M) log Na/Li = 1195/T + 0·38 These relationships, which at present are not well understood, result mainly from the increase of Li concentrations in waters with temperature.Equation (a) proved to be adequate for spring waters from mostly known geologic origin; this is an important feature in geochemical surveys for geothermal prospecting.Furthermore, when comparison between springs and drillhole chemistry of a given geothermal field is possible, the Na/Li geothermometer gives more reliable temperature estimates from the spring compositions than do classical geothermometers.     

Geochemistry and groundwater contamination in the La Selva geothermal system (Girona, Northeast Spain)

Hot spring waters of the La Selva geothermal system show high concentrations of Cl, F, Ca, Na, K, Li, Si, As, Ba, and Rb, whereas cold waters show low salinity, high concentrations of NO₃, and significant As content when mixed with geothermal waters.Modeling of the geothermal fluids indicates that the fluid is supersaturated with aragonite and calcite, which matches the travertine precipitation close to the present discharge areas. Moreover, the barite and fluorite are also are near equilibrium levels, indicating possible control of Ba and F solubility by these mineral phases, which also precipitate in some discharge areas. Likewise, the fluid is supersaturated with respect to quartz, indicating the possibility of siliceous precipitation near the discharge areas of the present geothermal fluids.Taking into account the Na-K, Na-K-Ca, and SiO₂-temperature geothermometers, the temperature of the reservoir may be estimated to be about 135 °C.The chemistry of the geothermal fluids has changed from a recent high-enthalpy system, which precipitated siliceous deposits, to the present low-enthalpy system, which precipitates carbonated deposits (travertine).Multivariate analysis of the groundwater shows high correlations between K, Ca, As, Br, Ag, and Ba, suggesting that As is introduced to the environment via geothermal fluids. Moreover, As concentrations in hot groundwater are associated with high concentrations of Li and Si, as has been observed in other geothermal fields. Metal concentrations in the hydrothermal deposits show high values of Ag, As, Ba, Pb, Sb, and Zn, mainly in the siliceous deposits of the town of Caldes de Malavella, where the geothermal system deposited materials with high As concentrations (123-441 ppm).The similarities between the geochemical characteristics of the hydrothermal deposits and the groundwater suggest that the metals in these deposits and fluids have the same origin.     

Field testing results of downhole scale inhibitor injection

The first field tests on the addition of scale inhibitors to geothermal brines were carried out in Italy between 1981 and 1985 at Cesano and at Latera. A long-term experiment was recently performed in the Latera 2 well to check the feasibility of the downhole inhibitor injection technique as a reliable solution to the carbonate scaling problem. A plastic-lined injection pipe was used to solve the corrosion problems caused by the inhibitor itself. Two different scale inhibitors have been tested down to minimum concentrations of 10 ppm. Downhole injection was performed at about 750 m depth using a 4.6 mm OD flexible pipe freely lowered in the 9″5/8 casing and with total flow rates of 300 t/h for three months.     

Reinjection studies of vapor-dominated systems

Reinjection of produced brines is currently being considered for Larderello and other vapor-dominated geothermal fields as a potential means for safe disposal and enhanced energy recovery. In this context is it necessary to develop a detailed assessment of the impact of injection on reservoir performance, in particular on power output and reservoir longevity.As a step towards such an assessment, the present work explores the effects of cold water injection into idealized model reservoirs using numerical simulation techniques. The rock matrix parameters and thermodynamic conditions employed are representative of the Larderello steam fields.One-dimensional radial flow near an injection well is modeled to study in detail the propagation of hydrodynamic and temperature fronts. Simulated results are subjected to single-phase pressure transient analysis to examine the applicability of this technique for determination of formation parameters.Gravity effects for injection into a thick two-phase reservoir are studied within a vertical two-dimensional mesh. Comparisons are made between shallow and deep injection.Mixed production/injection schemes are investigated for a five-spot geometry using an areal two-dimensional mesh. It is found that production pressures and power output change little due to injection, whereas longevity of the field can be substantially increased.A one-dimensional vertical column representing a cross-section of Larderello is used to study the effects of injection at different depths in the more depleted zones of this reservoir.     

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.     

Groundwater quality and geothermal energy. The case of Cerro Prieto Geothermal Field,México

The influence of the Cerro Prieto Geothermal Field (CPGF) on groundwater quality of the close-by agricultural area was evaluated by means of chemical and isotopic determinations. According to irrigation standards, concentrations of As, Cd, Pb, Crtot, Cr(VI), Cu, Cd, Hg, B in agricultural wells showed the suitability of the water for irrigation. Iron was below irrigation limits in all but one well. However, chloride levels were above those limits in 83 out of 87 collected samples. Isotopic determinations of δ²H, δ¹⁸O, δ³⁴S, δ¹³C, and spatial concentration trends of elements related with geothermal brines and toxic metals and metalloids did not indicate an influence of the CPGF to groundwater in the nearby agricultural area. Isotopic values of δ²H, δ¹⁸O showed the occurrence of evaporation processes and infiltration of canal's irrigation water to geothermal water reservoirs and to groundwater in the agricultural zone. High chloride concentrations might be associated with these processes.     

The used automobile catalytic converter as an efficient catalyst for removal of malathion through wet air oxidation process

The automobile catalytic converter (ACC) contains a huge number of precious metals as catalysts. When an ACC fails to meet standards, it is removed from the exhaust of an automobile but retains some catalytic activity. However, the recovery and/or activation of this waste is a high-cost process and includes several chemical treatments. Catalytic wet air oxidation (CWAO) has been reported as an effective wastewater treatment method. The most important disadvantage of CWAO is cost-nonefficiency. Herein, to overcome these problems, the simple recovery of catalysts from waste ACC for reuse in CWAO was investigated. The optimum conditions of reaction were investigated through response surface methodology (RSM). The optimum removal efficiency was 88% when the reaction conditions were set on the 20 bar of pressure at 111.5 °C over 77 min and using 0.41 g of recovered catalyst. In addition, toxicity testing was performed on a model of malathion-contaminated wastewater before and after CWAO treatment. Final product identification was performed which showed that CWAO eliminated the toxicity of wastewater and was determined to be malaoxon, present at acceptable concentrations, and tributyl phosphate. In conclusion, there may be important potential for the use of recovered ACC catalyst in the treatment of toxic wastewater.     

Hydrometallurgical separation of aluminium,cobalt, copper and lithium from spent Li-ion batteries

A hydrometallurgical route based on leaching-crystallization steps for the separation of metals Al, Co, Cu and Li from spent Li-ion batteries was evaluated in this paper. Once dismantled for the removal of both plastic and steel cases, the anode (containing mainly Cu) of such batteries was manually separated from the cathode (which contains Al, Co and Li) for the recovery of Cu. The metal content of both anode and cathode was assessed by X-ray diffraction (XRD), X-ray fluorescence (XRF) and atomic absorption analytical methods. The cathode was firstly leached with NaOH for the selective removal of Al, followed by leaching with H₂SO₄ + H₂O₂ for the dissolution of the remaining Co and Li. The operating variables concentration of NaOH and concentration of H₂O₂ were found significant for the metal dissolution conditions investigated at basic and acid leaching operations, respectively. On the other hand, the variables temperature and concentration of H₂SO₄ showed minor effects at acid leaching step. Reaction schemes were proposed to describe basic and acid leaching operations. The recovery of Co from the acid liquor was carried out by crystallization. This hydrometallurgical route was found to be simple and adequate to separate metals for recycling purposes.     

Impact of geothermal well testing on exposed vegetation in the Northern Negros Geothermal Project, Philippines

The impact of geothermal fluid discharges during the testing of Pataan 5-D well was evaluated on seedlings of mahogany (Swietenia macrophylla King) at various distances from the well and on natural forest vegetation around the wellpad. The parameters measured were: (1) geothermal brine spray concentration; (2) plant concentration of geothermal signature ions (B, Cl, Li and Na); (3) symptoms of plant damage; and (4) plant recovery. Meteorological parameters were also gathered. Adverse effects on the test plants were observed at distances of 5–50 m from the well silencer for over-spray during the horizontal discharge and at 50–350 m from the wellhead during the vertical discharge. Salinity was identified as a significant cause of plant damage. Observed symptoms of damage included drying of leaf tissues expressed as necrotic areas, which occurred first at the tip of older leaves and progressed along the margins as severity increased, resulting in abnormal defoliation. Recovery of seedlings and natural vegetation from sprays was observed in both vertical and horizontal discharges.     

Density functional theory study on hydrogen storage capacity of metal-embedded penta-octa-graphene

H₂ storage capabilities of penta-octa-graphene (POG) adorned by lightweight alkali metals (Li, Na, K), alkali earth metals (Be, Mg, Ca) and transition metals (Sc, Ti, V, Cr, Mn) are studied by density functional theory. Metals considered, with the exception of Be and Mg, can be stably adsorbed to POG, effectively avoiding metal clustering. The average H₂ adsorption energies are calculated in a range from 0.14 to 0.95 eV for Li (Na, K, Ca, Sc, Ti, V, Cr, Mn) decorated POG. Because the H₂ adsorption energies for reversible physical adsorption lie in the range of 0.15–0.60 eV and the desorption temperatures fall in the range of 233–333 K under the delivery pressure, 4Li@POG and 2Ti@POG are found to be the most suitable for H₂ storage at ambient temperature. By polarization and hybridization mechanisms, up to 3 and 5 hydrogen molecules are stably adsorbed around each Li and Ti, respectively. The H₂ gravimetric densities can reach up to 9.9 wt% and 6.5 wt% for Li and Ti decorated POG, respectively. Our findings suggest that, with metal decoration, such a novel two-dimensional carbon-based structure could be a promising medium for H₂ storage.     

Determination of·fouling factors for shell-and-tube type heat exchangers exposed to los azufres geothermal fluids

According to the latest estimates, there are about 1500 geothermal sites in Mexico, ninety percent of which can probably produce low enthalpy fluids only. Hot water discarded from geothermal flash plants adds to this stock which represents a considerable source of thermal energy. Its utilization for direct industrial applications or electricity generation through binary cycles requires heat exchangers.The IIE, with the financial support and technical cooperation of CFE, has for some time been experimenting with heaters of different types subject to geothermal brines. This paper describes the work done to date and the preliminary results obtained.     

冰岛Laugaland地热田热储回灌中水化学动态特征

水化学动态观测是地热田动态监测工作中一个重要组成部分。在热储回灌过程中,通过地热田水化学动态观测,能够及时发现和预见不利问题的发生。冰岛Laugaland地热田的示踪试验分析结果表明,开采井与回灌井之间水力联系密切。根据开采井的水化学动态资料,可以发现开采井中呈现明显的回灌水与“亲水”的混合迹象。基于水化学浓度质量平衡的计算结果表明,开采井中回灌水的平均回采率约为88.5%。     

Chemical thermodynamics in geothermal operations

Chemical thermodynamics of geothermal brines are important in every aspect of geothermal development, starting from initial stages of exploration to the final stages of utilization. Yet there are serious gaps in the knowledge of high temperature thermodynamics of aqueous fluids. The critical areas of chemical thermodynamics that need serious evaluation include: (1) chemical and physical characteristics of aqueous solutions at high temperatures, (2) solubility and phase behaviour of numerous inorganic solids in aqueous media at high temperatures, (3) solubility and flash behaviour of gases in equilibrium with aqueous media at high temperatures and (4) cement, metal and other material resistivity to any mechanical and/or chemical degradation in various high temperature aqueous environments. The present paper reviews the status of the various aspects of chemical thermodynamics. The emphasis is placed in reviewing the various methodologies used in predicting scale formation and gas flashing during the production of geothermal brines. Various well-known models used in obtaining the chemical thermodynamic information are also critically reviewed. The general lack of knowledge on the data bases related to solubility of various species in high temperature brine is clearly pointed out. Based on the critical review of chemical thermodynamics of geothermal brines, the following conclusions are made: 1. The basic chemical thermodynamics of aqueous systems at high temperatures are not well known. 2. There is a lack of a thorough and reliable data base related to the phase behaviour of inorganic solids and their solubilities in aqueous media at high temperatures. 3. The solubilities and flash behaviours of gases in equilibrium with aqueous media at high temperatures and high pressures are not well known.     

Developments in geothermal waste treatment biotechnology

Disposal of toxic solid waste in an environmentally and economically acceptable way may be in some cases a major impediment to large geothermal development. The major thrust of the R &D effort in this laboratory is to develop low-cost processes for the concentration and removal of toxic materials and metals from geothermal residues. In order to accomplish this, biochemical processes elaborated by certain microorganisms which live in extreme environments have served as models for a biotechnology. It has been shown that 80% or better removal of toxic metals can be achieved at fast rates (e.g., 25 hours or less) at acidic pH and temperatures of about 60°C. There are several process variables which have to be taken into consideration in the development of such biotechnology. These include reactor size and type, strain of microorganisms, biomass growth, temperature, loading concentrations of residual geothermal sludge, and chemical nature of metal salts present. Recent data generated by the research and development effort associated with the emerging biotechnology will be presented and discussed.     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

40 years of Dogger aquifer management in Ile-de-France, Paris Basin, France

Geothermal energy has been supplying heat to district networks in the Paris Basin for more than 40 years. The most serious difficulties have been corrosion and scaling related problems that occurred in many geothermal loops in the mid-1980s. The main target of all exploration and exploitation projects has been the Dogger aquifer. Most of the operating facilities use the “doublet” technology which consists of a closed loop with one production well and one injection well. Injection of the cooled brines leads to the progressive exhaustion of the resource at the local doublet scale. Consequently, most of the research effort has been focused on quantifying the temporal evolution of the cooling, and to forecast the lifetimes of doublets and the occurrence of the “thermal breakthrough”. At the turn of the 21st century, there was a revival of geothermal energy development in France and new projects are presently being considered. The 40 years of experience in geothermal exploitation of the Paris basin constitutes a firm basis upon which to devise a sustainable regional management approach for the geothermal resource. Several governmental policies seek to promote further geothermal development of the Dogger aquifer with structures in place to facilitate technical studies.     

Chilean geothermal resources and their possible utilization

Most of the hot spring areas in Chile are located along the Andean Cordillera, associated with Quaternary volcanism. The volcanic—geothermal activity is mainly controlled by the subduction processes of the Nazca and Antarctic oceanic plates under the South America continental plate, and occurs at three well-defined zones of the Chilean Andes: the northern zone (17°30′–28°S), the central—south zone (33φ–46°S) and the southern-most or Austral zone (48°–56°S).Some tested high temperature geothermal fields, and geological and geochemical surveys of many other hot spring areas, evidence a great potential of geothermal resources in this country. Both electrical and non-electrical applications of this potential are considered in this paper.Taking into account the potentially available geothermal resources, the development of natural resources, the geographic and social—economic conditions existing in the different regions of Chile, it is concluded that power generation, desalination of geothermal waters, recovery of chemicals from evaporite deposits and brines and sulfur-refining are the main possible applications of geothermal energy in northern Chile; in central—south Chile geothermal energy is suitable for agribusiness such as greenhouses, aquaculture and animal husbandry.     

Interfaces between geothermal brine-induced scales and SiC-FILLED polymer LININGS

Silicon carbide (SiC) grit-filled polymeric materials with high thermal conductivity can be used to line carbon-steel heat-exchanger tubes in geothermal power plants at moderate temperatures and to improve resistance to corrosion. The susceptibility of ester groups within the polymers to a reaction with Ba, which is among the chemical ingredients of some geothermal brines, is a critical issue for this lining material because of the formation of Ba-complexed carboxylate hydrolysates. Such hydrolysates promote the deposition of brine-induced scales.