New water management plan for the the Terrafame mine – possibility of significant benefits 16.6.2016
- The new water management solutions would reduce the environmental impacts of the Terrafame mine and improve production efficiency and could bring new business opportunities.
- The concept plan includes significant changes in the mines sulphate, sodium and sulphur management and chemicals recycling.
- The water management development project continues as a pilot-scale research and development phase and upscaling.
Terrafame Group in cooperation with the Terrafame mine has prepared a new concept for water management which would reduce the environmental impacts of the Sotkamo mine as well as significantly improve its production efficiency and business potential.
The concept is the result of the water management development project which was started in autumn 2015 and which aimed to find solutions from experts in the field of water and chemicals for reducing the sulphate concentration in the waters discharged from the mine. In the spring of 2016, the project progressed to demonstration phase where the proposed solutions were tested in practice at the Terrafame mine.
New opportunities to develop the production process
Developed on the basis of the results of the demonstration phase, the plan is based on reducing the use of or replacing the substances that increase sulphate concentration or interfere with sulphate removal. In addition, the concept is based on recycling sulphate in the production process. The new solutions would possibly lead to substantial changes in the different stages of the Terrafame production process.
We are very pleased to see such a significant new plan achieved in the demonstration phase of the water management project on a tight schedule. The key changes would include partial or complete replacement of sodium hydroxide (NaOH), used as a neutralizing agent in the process, with potassium hydroxide (KOH). The sulphate in the purified waters discharged from the mine is caused mainly by the sodium hydroxide, as the sodium it contains binds sulphate and thus reduces the effectiveness of the lime treatment used in water purification with regard to the sulphate, says Jani Kiuru, Project Director of the water management development project at Terrafame Group Ltd.
Replacement of sodium hydroxide would increase the chemical costs of the mine. Therefore, the metals recovery plant process would be changed in the concept to utilize the value of the neutralizing chemicals. The changes are related to management of process flows and upgrade of the reverse osmosis plant as well as to setting up entirely new processes parts.
Regarding solution flow at the metals recovery plant, the concept would mean shutting down the return solution flow to the bioleaching heaps. The increased amount of water caused by this change could be treated in the current reverse osmosis plant after its capacity is increased through modifying the processes. The potassium sulphate extracted in the reverse osmosis plant could be treated further for example by using forward osmosis or evaporation. The potassium sulphate could be sold as raw material for the fertilizer industry, for example. Alternatively, the concentrate could be fed into the bioreactor in order to process the potassium into potassium carbonate. Also potassium carbonate is used as fertilizer. The sulphur generated in the process could be utilized in the precipitation of metals.
Terrafame Group has protected the concept introduced here and a number of individual inventions included therein. In addition, the parties involved in the development project have patents and applications related to their respective technologies.
A more detailed description of the proposed changes to the process is presented in the appendix at the end of this press release.
Significant benefits for environment and economy
The new water management solutions would significantly reduce the environmental impacts of the mine as well as improve its production efficiency and business potential. Concrete benefits would include, for instance, greater water treatment capacity and significantly reduced sulphate and sodium load in the waterways. The new water management concept could also introduce new commercial opportunities.
The environmental impacts of the mine would decrease significantly as the amount of sulphate would drop to a fraction of the current amount, Kiuru says.
The development project continues as a pilot-scale research and development phase, technical and economic evaluation and upscaling. Based on our assessment, the development and planning phase at the Terrafame mine would be completed by the end of 2017, in which case setting up pilot production could start at the beginning of 2018, says Matti Hietanen, CEO of Terrafame Group Ltd.
Based on the preliminary estimates, it seems that the financial result of the operations could improve clearly as a result of modifying water loops and chemical flows as well as gaining additional revenue from new products, such as fertilizer raw materials generated as by-products of the production process. Annually, the impact on the result could be as high as tens of millions of euros, Hietanen says.
Terrafame and Terrafame Group are currently assessing the investments into the mining area and the production process that are required by the presented water management solutions. The estimates regarding cost savings and new business opportunities will naturally be specified later following the technical and economic analysis, Hietanen concludes.
Innovative solutions, proven technology and eight proposed solutions behind the new concept
The water management development project launched a public consultation, seeking solutions from experts in the field of water and chemicals for reducing the sulphate concentration in the waters discharged from the Sotkamo mine. Terrafame Group received more than 100 viable proposals, of which eight projects were selected to participate in the demonstration phase. The new water management concept has utilized the results of the demonstration phase, the knowledge of viable commercial solutions, new innovations and solution models from other industries and has applied all of these to local conditions at the mine and to the unique production process.
Terrafame Group chose the proposed solutions for the pilot using the reviews of the water management development projects steering group. The water management development projects steering group comprises leading Finnish water specialists from several organizations, such as VTT Technical Research Centre of Finland, GTK Geological Survey of Finland, the Finnish Water Forum, Aalto University, Lappeenranta University of Technology and the University of Oulu.
Aquaminerals Finland Oy will demonstrate with laboratory experiments e.g. adsorbent performance in the process waters to improve the efficiency of the reverse osmosis plant.
Oulu Water Alliance Oy and Adven Oy will demonstrate a combination of evaporation and crystallisation. The aim is to develop a concept in which the waters of the metals recovery plant will be evaporated and metal sulphates will be crystallised from the retentate at a later stage.
Sulfator Oy will demonstrate the effectiveness of the bioreactor in sulphate removal. The experiments will be performed in a pilot at the Savonia University of Applied Sciences. If operational, the method would provide an energy-efficient way to significantly reduce the sulfate concentration in the waters discharged from the mine.
Outotec Plc will demonstrate the effectiveness of freeze crystallisation together with a Dutch industry operator, EFC Separations BV. The idea is to take advantage of the cold conditions of the Arctic region in sulphate crystallisation by freezing the salts.
Sofi Filtration Oy will demonstrate the suitability of its filter in two different process stages: the pre-treatment of the RO plant and the precipitation of metals.
Skyscape Oy is developing concepts for being able to recycle the reject, i.e. the water removed from the RO plant, in the process. Other concepts being investigated include, among others, solutions related to optimisation of chemicals and metals recovery.
Suomen Tarkkuusvalimo Oys project focuses on the preliminary study of evaporation. The demonstration will examine commercial evaporation solutions and their suitability for the mines processes. In the demo, experiments will be conducted to study critical phenomena with regards to evaporation, such as precipitation, heat transfer and corrosion.
Technical Research Centre of Finland VTT Oy in its proposal examines the possibility of replacing the sodium hydroxide with an alternative neutralizing agent in metals precipitation. If operational, the amount of sodium hydroxide could be reduced, enabling a more efficient removal of sulphate with gypsum sedimentation.
Water management development project schedule and next steps
The water management development project will be carried out in phases, progressing from mapping of technologies through the pilot and demonstration phase to the actual planning and construction phase.
In the first phase (mini-demonstration phase) in winter and spring 2016, Terrafame Group evaluated and selected a set of potential solutions and provided financing for their developers. The applicability of the solutions to a mining environment has been studied in smaller separate projects.
In the second phase (concept development), an integrated, comprehensive concept will be built on the basis of these solutions by the beginning of 2017. After concept development, the concept will undergo a feasibility study and its scale-up will begin.
The development and planning phase is expected to be completed by the end of 2017 so that construction of a demo plant could start in the beginning of 2018.
Terrafame Group Ltd.
Project Director Jani Kiuru, Tel. +358 40 823 8471, firstname.lastname@example.org
CEO Matti Hietanen, Tel. +358 40 823 8806, email@example.com
Terrafame Group Ltd. is a special-purpose company wholly owned by the State of Finland. It is responsible for managing the state ownership and exercising the owner's power at Terrafame Ltd. Terrafame Group's role is to secure private supplementary financing and support the stabilisation and development of the mining company's operations. Terrafame Group is also responsible for helping the development of new technological solutions related to mine water purification.
Terrafame Ltd. is a Finnish mining company producing primarily nickel and zinc by bioheapleaching at its mine located in Sotkamo. The aim is environmentally sustainable, safe and economically viable mining operations. Terrafame is owned by Terrafame Group Ltd.
An Energy Efficient Sulphate Removal Concept for Hydrometallurgical Processes
Based on laboratory and pilot-scale studies a new concept for water treatment in mining operations was created. This concept will reduce significantly the sulphate load to nature and at the same time reduce operational costs of the mining. Altogether this approach will enable economically attractive and sustainably positive way to produce metals and process waters.
The new concept consists of a sequence of modification applied into existing process at Terrafame´s multi-metal mine at Sotkamo, Finland. The applicability of the concept is not limited to this process only but can be utilized in any water-intensive process using large quantities of liquid chemicals. The modified process with the modifications indicated with numbers is illustrated in Figure 1.
Figure 1. Hydrometallurgical process at Terrafame, Sotkamo mine with modifications included. The numbers indicate the modifications as follows:
- Changes in applied chemistries in metals recovery
- Capacity and performance modifications at reverse osmosis (RO) plant
- New unit process to concentrate the RO retentate
- New unit process to further process the retentate
- Recovery of additional by-product from the water treatment waste
The modifications in details are:
ALKALINE SWITCH (1):
Neutralization phases at the metals recovery are being carried out using sodium hydroxide (NaOH). This leads to excess flow of sodium to the water treatment. Sodium binds certain amount of sulfate and complicates the removal of sulfate from the discharged waters. Current water-purification technology – lime treatment – is not able to precipitate sulfates bind with sodium. Therefore NaOH is replaced with an alternative alkaline in this concept. Primary this alternative alkaline is potassium hydroxide (KOH).
RO RATIONALIZATION (2):
The alkaline switch leads to increased water flow to the RO-plant since the return flow from the metals recovery to the heaps needs to be shut down in order to not to lose the valuable cations (K+ in the case of KOH) to the heaps. RO rationalization is carried out to ensure stable and qualitatively acceptable flow to the forthcoming processes and to increase the RO capacity to the required level.
RETENTATE THICKENING (3):
Increased capacity increases operational costs and at the same time, the modifications increase the amount of impurities in the permeate of the membrane processes. The economy as well as the separation especially related to calcium will be improved. The retentate concentration creates an additional flow of purified water to be utilized in the earlier phase of the process. Primary the concept utilizes forward osmosis (FO) technology to concentrate the RO retentate. In the FO osmotic pressure draws the water molecules through the membrane to a draw solution. In this concept the draw solution is sulfuric acid dosed to the heaps to adjust the pH value of the flow solution. The FO technology can be replaced by any other unit process performing the retentate thickening. The options are for instance multi-stage RO, evaporation, crystallization, freeze crystallization, and adsorption. The thickening technology is adaptable to any other process stage as well.
RETENTATE PROCESSING (4):
At this stage the flow consists of concentrated solution of sulphate and potassium. The potassium sulphate solution can be used as such as raw material for the fertilizer industry, for example. In case the bioreactor is applied the reactor converts the feed to potassium carbonate and hydrogen sulphide. In case of evaporation or crystallization the outcome is potassium sulphate.
BY-PRODUCT RECOVERY (5):
From the stage (4) the potassium chemicals can be utilized as fertilizers or fertilizer raw materials whereas the hydrogen sulphide can be returned to the metals recovery to adjust the pH in metals precipitation.