Geochemical Engineering:
Natural Solutions for Environmental Problems

By Prof. Dr emeritus R.D. Schuiling and Dr. J.J.P. Zijlstra
May 2001

The Authors are research scientists at Geochem Research BV in De Bilt, the Netherlands. This organisation has over 15 years experience in environmental management, and applies their knowledge of geochemistry and mineralogy to find cost-effective solutions for environmental problems. A selection of projects comprises: Treatment of Jarosite waste from the Zinc industry; Removal of Phosphate from manure by means of Struvite precipitation; Removal of Heavy Metals (Cu, Zn, As,...) and neutralization of Acid Mine Water by means of sorption on pelletized Red Mud filters and; Neutralization of AMW with Olivine.

Geochemical engineers develop cost-effective methods to remediate pollution in the natural environment. They are inspired by nature and use the knowledge of geochemists about the geochemical cycle and the interaction between minerals and chemical compounds in solution. A large number of examples of current geochemical engineering applications are presented, which elucidate the role of geochemical engineering in modern environmental management.

Contents

Introduction

Geochemical engineering is a rather new discipline in environmental management. It recently evolved from geochemistry, a fundamental science concerned with the chemistry of the earth. Geochemical engineers study the properties of minerals, soils, rocks, waters and natural chemical processes, in order to find cost-effective solutions for environmental problems. Although geochemical engineers use the same instruments as chemical engineers and also perform tests and experiments in the laboratory, it is mainly nature that inspires them, when conceiving innovative environmental technologies.

Geochemical engineers realize that any harmful substance produced by industry will eventually enter the environment and become part of the geochemical cycle. In nature, numerous substances are found that have the same toxic properties as anthropogenic pollutants and yet these often pose no serious problem to the health of human beings and life in general. This is so, because these substances occur in low concentrations or, if they are highly concentrated, they are not mobile and not available to organisms.

We do not yet fully understand the precise mechanisms that control the distribution of toxic substances in nature. Too often government and environmental protection agencies impose environmental legislation and use environmental management technologies, that are not very effective in the best case, or even dangerous in the worst cases. Often this is a consequence of our lack of understanding concerning the natural chemical processes that characterize the geochemical cycle. As an example of the importance of geochemical investigation and the problems that may arise if one does not take the natural chemical processes into consideration, we present a case that occurred recently in the small town of Baarlo (The Netherlands).

Several decades ago, the chemical industry used to dump its toxic waste in the ground and simply cover it up. As the population density rose in the Netherlands, municipalities claimed the same land for habitation. After a while, however, the new inhabitants started to complain about strange smells and curious diseases. Billions of dollars had to be spent to clean up these toxic sites. One can imagine the panic that arose when the municipality of Baarlo discovered concentrations of the very toxic arsenic on their land, which were in the order of 1400 mg/kg, about 30 times as high as the sanitation norm of 50 mg/kg imposed by the government. First it was suggested that farmers had illegally dumped large quantities of arsenic-bearing fungicides in the past, and preparations were made to remove this toxic waste at great cost. Fortunately, however, the municipality was wise enough to ask also the advice from a geochemist. A site investigation showed that the high arsenic values occurred in an iron-rich soil horizon, and were due to natural causes.

At this site, reducing groundwater with perfectly normal iron and arsenic concentrations, a few mg and microgram per liter, respectively, rises to the surface and is oxidized in contact with the air. The arsenic becomes insoluble and is rendered completely harmless as it is immobilized in a stable FeAsO4 complex. Removal of the soil would be of no use, because a new layer with high arsenic concentration would have started to form immediately afterwards, as the flow of groundwater could not be stopped. The town council of Baarlo wisely decided not to remediate the site, and to proceed with the expansion of the town, notwithstanding the fact that the arsenic content of the soil was above the legally admissible norm.

A good understanding of the geochemical environment is important, not only for the distinction between natural and anthropogenic pollution, but also for the recognition of natural processes that may serve as an example for the development of innovative environmental technologies. For instance, one may consider the acid lake at Armyansk (Crimea, Ukraine), where waste sulfuric acid is discharged in a ponded shallow bay. Due to equilibrium between the volume of water evaporated in a dry climate and volume of acid discharged, acidity increases continuously. However, no acid leaks to the groundwater as it reacts with carbonate in underlying clays. As a consequence of this reaction, an impermeable hardpan of gypsum and iron hydroxide is formed. gypsum has a molar volume that is twice as large as that of the dissolved carbonate, and thus the pores of the clay are effectively sealed. This observation of a 'natural' self-sealing process gave rise to the development of new types of liners for landfills. Additionally, it inspired the development of a method to neutralize waste sulfuric acid and raise the earth surface artificially, by means of sulfuric acid injection into subsurface limestone reservoirs. During the injection of several thousand liters of sulfuric acid in a field experiment, it was shown that the newly formed gypsum is able to expand the subsurface limestone reservoir, and to lift the earth surface above. Simultaneously, toxic metals can be incorporated in the gypsum, or precipitated as hydroxides at the reaction front where the pH steeply rises. Likewise, polluted Acid Mine Drainage, that is sulfuric acid with high concentrations of metals which is produced during the oxidation of metal sulfide ore, can be injected into subsurface limestone. The principle of rock expansion can also be used in the prevention of the seepage of AMD from mine shafts and galleries, simply by filling these with crushed limestone which will form an expanding and self-sealing plug on reaction with AMD.

In this contribution we shall elucidate the principles of geochemical engineering with the help of several other examples that have a worldwide application. Most of these examples concern geochemical engineering methods, that have been conceived by emeritus Prof. Dr. R.D. Schuiling, and that are developed in cooperation with his colleagues at the Utrecht University (Utrecht, The Netherlands), at the International Institute for Hydraulic and Environmental Engineering (Delft, The Netherlands)(1), and at Geochem Research B.V. (De Bilt, The Netherlands)(2). Part of this text has been published before and the examples and related subjects have been described more elaborately elsewhere (Vriend & Zijlstra, 1998)(3).

Environmental Problems

Environmental problems are encountered if the concentrations of mobile substances, available to organisms, are either too low or too high. Many elements play an essential role in the physiology of plants, animals and men. Apart from the major elements H, C, N, O, P, S, Ca and Fe, these include Li, B, F, Na, Mg, Cl, K, V, Mn, Co, Ni, Cu, Zn, Se, I, Mo and probably several others. Most organisms are adapted to the range of concentrations commonly encountered in nature. Geo-diversity is the natural counterpart of bio-diversity and one may consider it an important condition for and cause of bio-diversity. At the extreme ends of the concentration range we find environments that are lethal to many organisms, but in which certain organisms find their natural niche. The occurrence of extreme concentrations of hazardous components in certain parts of our environment has not exclusively originated by the activities of men, but is as old as the earth. Poisonous gases associated with volcanic eruptions, sulfuric acid from volcanoes or from the oxidation of sulfides, high concentrations of heavy metals in ore deposits and toxic levels of fluorine or arsenic in ground waters are all generated by common geologic processes. Many of the concentrations forming in nature would be considered as environmental hazards if originating from human activities.

Geochemical Engineering Solutions

Even so, there are many sites that are polluted by human activities to such a degree, that they constitute a real threat to the local ecosystem. If we cannot prevent anthropogenic pollution, remediation measures have to be taken to restore the natural conditions. These measures should mainly be concerned with ways to reduce pollutant levels in the bio-available, mobile phase, and they fall under the following five categories:

  1. Breakdown, neutralization or decay
  2. Concentration
  3. Dilution
  4. Isolation
  5. Immobilization

By studying the ways in which these processes take place in nature, we can learn how to devise efficient, inexpensive and environmentally safe technologies.

Rate of Reaction in Geochemical Engineering

A major concern in the design of any technological process is the rate at which it proceeds. Slow reactions require large reactors to attain a certain production. In environmental technology this can also be problematic, as public pressure demands the fast clean up of a polluted site. Geochemical processes may be very slow and this disadvantage has to be compensated. There are essentially two ways to handle this problem. The first is to speed up the reaction rate by increasing the temperature, increasing the reactant surface by grinding, increasing the strength of solutions and/or adding a catalyst. The second approach is to accept the slow reaction and reduce the costs of the environmental technology. Nature provides its own reactor and pollution is treated in situ. Space and time constraints become less severe and personnel costs are limited, as the process is a self-remediation, requiring only minimal supervision and monitoring.

Experience with current environmental technologies shows that, while the applied technology itself may be fast, unexpected side effects may require additional costly and time-consuming measures. Only a fraction of the technologies that are effective on a laboratory scale, perform equally well under field conditions. These problems are often related to the fact that the applied process turns out to be incompatible with the inherent properties and local conditions of the treated natural system, a disadvantage that may be overcome by adhering to geochemical engineering principles.

Scales of Geochemical Engineering

Geochemical processes act on many different scales, from the surface of a mineral to global processes affecting the whole hydrosphere or atmosphere. In order to device an efficient strategy to combat environmental pollution on any spatial and temporal scale, it is necessary to understand the geochemical cycle, and to design methods that fit into the natural cycle.

Global Opportunities for Geochemical Engineering

The 'Western' countries, including USA, Canada, Western Europe and Japan, have a strong and diversified industry. Per capita income is higher than in the rest of the world, and this leads to a consumption society. Because there is a high production and consumption, including a high turnover rate of (not so) durable goods, waste production and energy consumption are also high. Environmental regulation and the enforcement of environmental laws are quite advanced, and there is a large amount of money available for the environment. Salaries are high, which means that environmental technologies must be automated to a high degree and should lead to rapid results. A major factor in the compliance with environmental regulations is the fact that industries in the West do not like to be known as polluters. This stems at least as much from economic considerations as from a moral sense of responsibility. Thus, more and more it can be seen that industries solve their environmental problems in close cooperation with government agencies.

The economy of the 'Eastern' countries, in particular Russia and former Soviet states, depended strongly on heavy industry, and the associated environmental problems are enormous. In the old system, emphasis was on production, and not on waste management or environment. Environmental awareness and environmental regulation have certainly improved in recent years, but enforcement is still weak. The authorities realize that a strict environmental policy would lead to the closure of many industries, and to further economic collapse. Even so, a better discipline by the plants would already go a long way to improve the environmental situation, and may even in the short run improve the economy of the industry at no extra cost. A major problem, of course, is that many industries are old, use outdated and polluting technologies, and have no capital for renovation.

In the emerging economies, such as India, Korea, Taiwan, Indonesia and Brazil, faced with high birth rates, governments pay much attention to rapid industrialization to improve the standard of living. Too often it is considered that any money spent on the environment is lost for industrialization. The lesson that the Western countries have learned the hard way, that it is much more expensive to clean up a mess, than to avoid it in the first place, goes unheeded in these quarters. The industries here realize that cleaner production leads to more cost-effective operations, which require fewer raw materials and less energy. However, cleaner production requires investment, which is not always available. The People´s Republic of China sets, to a certain extent, a positive example, as it is the official policy of China´s government that economy and environment should be developed simultaneously and in harmony.

The environmental problems of the last category, the have-nots, are again different. Very often these countries, like Bolivia, Columbia, and many African States rely heavily on one or two commodities only (e.g. oil, coffee, cacao, copper, tin). In a year that such commodities fetch a reasonable price on the world market, their economies can barely keep up, in poor years they are a disaster. These countries cannot afford strict environmental regulations, or are not capable to impose them properly. Polluting mining practices, including the uncontrolled release of mining wastes, as well as the non-expert use in agriculture of dangerous and persistent pesticides, which are banned in the West, are common. It is exactly this lack of environmental control, as well as the low wages, which attract some heavily polluting industries. Some of the worst practices have alarmed world opinion and provoke courageous battles waged by worried responsible citizens.

Geochemical engineering solutions, as compared to other environmental technologies, are natural solutions that can be applied in any country. The local climatic and geologic conditions define the best solutions to environmental problems, and not so much gross per capita income, the degree of industrialization, or the sophistication of government.

Many geochemical engineering solutions do not require high-tech equipment, which may not function well under conditions of large voltage fluctuations, frequent power failures, and in absence of facilities for repair and maintenance. Geochemical engineering solutions require little energy, they make use of locally available raw materials, and make optimum use of the prevailing climatic conditions.

Conclusion

Geochemistry concerns the investigation of natural chemical materials and reactions in and on the Earth. A geochemical engineer applies this fundamental understanding by designing methods that aim at the most efficient transformation of an undesirable into a desirable chemical environment. Although geochemical engineering is closely related to chemical and civil engineering, it is distinguished by its use of natural minerals in addition to industrial chemicals, and by the development of large-scale, long-term processes in the natural environment, in addition to the small-scale, short-term industrial processes. Geochemical engineering is an attitude of geochemists that recognize the need of the efficient use of limited resources; the development of alternatives and the design of closed production and recycling, or open production that fits in the natural geochemical cycle. Geochemical engineering requires close cooperation between the geochemist who understands the implication of natural processes for the industry, and the chemical engineer who wishes to improve the design of industrial processes, using nature as an example.

It has been shown that good solutions to waste problems have to fit into the natural environment and the geochemical cycle. Some important principles have been discussed and they can be summarized as follows: toxic chemical substances are only dangerous if they occur in the bio-available mobile phase, and at concentrations that exceed certain critical values. It is not possible to isolate toxic waste forever in the dynamic geologic environment, and efforts to do so are costly and bound to fail. A proper sequence of measures is required, when dealing with environmental pollution. These measures are dictated by natural, technological and economic constraints. Most important, the amount of raw material that is used and the amount of waste that is produced, have to be minimized. Maximum effort should be undertaken to prevent waste from polluting the environment, by adhering to the method of concentration and waste recycling. Preferentially, the waste from one industry should be used as a raw material in another industry. By mixing waste, applying a waste to waste technology, it can be transformed into a useful raw material, or else rendered harmless. If the above mentioned options have been exhausted, then one starts with the break down of waste into harmless natural components. Finally, if any waste is left, one tries to keep the concentration below the critical concentration in the bio-available mobile phase. This is done by means of dilution, immobilization, and, at last, by semi-isolation with an inevitable, but controlled release of pollutants.

By discussion of several examples, it was shown that cost-effective and sustainable handling of waste requires a good understanding of the geodynamics of the Earth. This involves knowledge of the catalysis of chemical reactions by bacteria and plants in phyto-remediation, and knowledge of the chemical reactions between minerals and mobile pollutants in water and air. It is recognized that a long-term solution of environmental problems concerns the involvement of thermodynamic stable minerals as part of the geochemical cycle.

It is hoped that the presented examples do elucidate the principles of geochemical engineering and inspire young scientists to develop new methods of their own. Methods that will find their way, not only in the western society, but also in the developing world. It should be realized that the larger part of the environmental problems is yet to be expected, as developing countries strive to reach living standards of the modern post-industrial society. It seems impossible to return to a pristine environment, like it existed before the arrival of Mankind. Nowadays, we are influencing the course of events on a worldwide scale. Therefore, we also have to learn to control environmental processes on a worldwide scale. It is inevitable that we will make mistakes, however, this cannot be an argument to lean back and remain idle, to refrain from drastic measures out of fear, or to neglect our responsibility for the well-being of future generations. We are confident that geochemical engineering will play an important role in our future and that it shall contribute to a sophisticated management of our natural environment on a global scale.

Acknowledgement

The authors thank Rein van Enk and Huig Bergsma for critically reading earlier drafts of this contribution and for their constructive advise.

References

  1. IHE/Delft. www.ihe.nl (schuilin@geo.uu.nl)
  2. Geochem Research B.V. geochem_research.tripod.com/geochem_research/ (research@geochem.nl)
  3. S.P. Vriend and J.J.P. Zijlstra (eds.), 1998. Geochemical Engineering: Current Applications and Future Trends, Elsevier Scientific Publications, Amsterdam. 350 pp. (vriend@geo.uu.nl)

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