Towards the sustainable development of the regional phosphorus resources industry in China: A system dynamics approach

Resources, Conservation & Recycling 126 (2017) 186–197

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Towards the sustainable development of the regional phosphorus resources industry in China: A system dynamics approach

MARK

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Zhibo Luoa, Shujie Maa,b, Shanying Hua, , Dingjiang Chena a b

Center for Industrial Ecology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China Department of Resources & Environment Business, China International Engineering Consulting Corporation, Beijing 100048, China

A R T I C L E I N F O

A B S T R A C T

Keywords: Phosphorus resources System dynamics Industrial transformation Resource productivity Ecological efficiency Policy implications

The explosive growth of the phosphorus resources industry in China has led to a series of problems (e.g., resource depletion, market supply and demand imbalances and environmental pollution). It is necessary to analyze the bottleneck in the development of the phosphorus resources industry under traditional modes and to suggest new directions for development. Therefore, this paper presents a system dynamics model based on the state of the regional phosphorus resources industry that focuses on resource, industrial, economic, environmental and social subsystems. Furthermore, by focusing on and quantitatively expressing the tailings recovery and resource reuse module, market regulation and elimination mechanism structures, governmental support and environmental constraints of game structures, and feedback structures between social innovation and industrial production, we construct a transformation mode as a development strategy for the phosphorus resources industry. The results demonstrate that the service life of phosphate rock under the transformation mode can be extended by 31 years. Compared to the 2014 levels, the resource productivity and ecological efficiency levels achieved can be increased by 2-fold and 2.5-fold in 2025, respectively. In addition, the social satisfaction levels can rise by roughly 50% under the transformation mode. Thus, the model can be used to assess the effects of various policies and to support decision making on development and environmental protection strategies.

1. Introduction Phosphorus plays an extremely important functionality of animal and plant (Soetan et al., 2010). Phosphate rock (PR) is an important strategic resource that can be used for the production of phosphate fertilizers (PFs), detergent additives, feed additives, flame retardants, water treatment chemicals and other chemical products (Corbridge, 2013). Unlike carbon and nitrogen, which undergo biogeochemical cycles, phosphorus is a non-renewable and irreplaceable mineral resource. According to the U.S. Geological Survey (Jewell and Kimball, 2014), by the end of 2012, the global and Chinese PR reserves reached 67 billion tons (Bt) and 3.7 Bt, accounting for 5.5% of Chinese reserves. China's PR is distributed across 27 provinces and autonomous regions, of which Yunnan, Hubei, Guizhou, Sichuan and Hunan serve as phosphate enrichment areas. However, the average grade of Chinese PR is only 17% and high grade PR is scarce (Sun, 2013). Since the 21 st century, China's PF production levels have increased gradually. According to the China Statistical Yearbook (Sheng, 2014), China's PF production levels increased from 1.2062 million tons (Mt) in 2005 to 17.4301 Mt in 2014 (100% P2O5). Since 2007, China has become a PF

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Corresponding author. E-mail address: [email protected] (S. Hu).

http://dx.doi.org/10.1016/j.resconrec.2017.07.018 Received 11 April 2017; Received in revised form 3 July 2017; Accepted 17 July 2017 0921-3449/ © 2017 Elsevier B.V. All rights reserved.

exporter. China's considerable growth in its exploitation of resources and in environmental pollution problems has also been highlighted. Some scholars estimate that China's PR resources will be depleted within the next 50–60 years (Cooper et al., 2011). At present, the sustainable development of the domestic phosphorus resources industry is facing several difficulties (Rawashdeh and Maxwell, 2011), such as shortages of phosphate resources, domestic and international, expansion of international PF production capacities, serious overcapacities within the domestic PF industry and serious environmental pollution problems resulting from industrial development. Due to pressure from resource depletion and environmental stress, the sustainable development of industry research is very important, such as efficient use of agricultural fertilizers, phosphorus product industry chain extension (Roberts and Johnston, 2015). Scholars have carried out corresponding research at the macro (national), meso (regional) and micro (firm) scales (Chowdhury et al., 2014). It has been noted that different analysis methods should be applied when examining different geographical areas and scales to evaluate phosphorus resource flows and management systems. At the macro level, studies have focused on the supply of

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phosphorus resources (Ulrich, 2016), on flow metabolism (Scholz et al., 2013), and on soil and river basin deposits (Villalba et al., 2008). For example, Van Vuuren et al. (Van Vuuren et al., 2010) analyzed phosphorus resource demand levels from 1970 to 2100 by simulating a phosphorus consumption scenario. Accordingly, by the end of the century (2100), depletion of the global PR base was predicted to reach 20–35% under the optimal conditions and 40–60% under the pessimistic conditions based on the current resource base in 2008. Ma et al. (Ma et al., 2012) studied the dynamic characteristics of China’s phosphorus resource metabolism for 1980–2008, analyzed related effects and put forward corresponding policy suggestions. At the meso-scale, the study focuses on the recovery of phosphorus resources in urban waste (Egle et al., 2015), the flow of phosphorus resources (Wu et al., 2016), phosphorus recovery and utilization in the steel industry slag (Lin et al., 2014). Yokoyama (Matsubae-Yokoyama et al., 2009) studied the Japanese steel industry phosphorus element recycling, with a view to supplement the reserves of phosphorus resources. At the micro level, studies have paid more attention to the innovation of specific production technologies, enterprise-level product adjustments and production optimizations and integration technologies (Song et al., 2014). Ma et al.’s (Ma et al., 2015b) study of the comprehensive recycling of phosphorus products and of associated resources serves as an example. At present, the following problems still plague research on phosphorus resources.

trends and by analyzing simulation results. Even when there is a shortage of real system data and multiple feedback structures change parameters within a controllable range, overall SD trends are not affected (Nordhaus, 1973). The process of SD modeling is illustrated in the Appendix file and the steps are shown in Fig. S1. At present, research on SD is mainly focused on the sustainable development of energy resources (such as coal, oil and natural gas (Hosseini and Shakouri, 2016; Liu et al., 2015b; Wu et al., 2015)) and on regional ecological environment management (such as urban pollution control and construction waste disposal (Marzouk and Azab, 2014; Rehan et al., 2011)). In the phosphorus resource related subject, it has not been reported about studying phosphorus resources at industry linkage level in China based on SD approach. In this paper, a general SD model is established based on the traditional industrial process system and bottlenecks affecting the development of the phosphorus resources industry (Section 2). Flow directions and interactions between material and information flows are expressed quantitatively based on typical problems of each link in the whole life cycle. In the SD model, we construct a market regulation and elimination mechanism structure, government support and environment restraint game structures, and a feedback structure between social innovation (including the innovation of enterprise, industry and academia, the innovation of support service system and the cultural innovation) and industrial production subsystems. Thereafter, the SD model is applied to Guizhou Province, China (Section 3). By a following comparison of different development paths of traditional and transformation modes, the effects of resources, industries, the economy, the environment and society are then compared in two development modes (Section 4). Finally, some suggestions for the sustainable development of the phosphorus resource industry are put forward (Section 5).

1) The relationship between government industrial policies and the development of the phosphorus resources industry is weak. 2) Research stresses the leading role of the government and pays less attention to market regulation and elimination mechanisms. 3) Most scholars use single phosphorus elements as the object of study and study the storage and loss of PR reserves and static phosphorus element metabolism from the perspective of environmental management. 4) Research stresses how new technologies can solve environmental pollution problems, yet there is a lack in government support and environmental constraint in terms of forcing industrial transformation and upgrading. 5) Regarding the consumption and application of phosphorus products, studies have paid less attention to downstream market demand forecasting. 6) Existing research lacks a discussion on the structure of feedback between social innovation and industrial production subsystems.

2. System dynamics framework 2.1. System description 2.1.1. Structure analysis of phosphorus resources industry The phosphorus resources industry chain mainly involves phosphate mining, dressing, processing and post-sale which represented by white blocks in Fig. 1. The material flow between modules is indicated by solid lines. The mutual effects of the subsystems and comprehensive indicators through interactions of information and material flows are shown by dotted line. The processing industry involves two main processes, namely thermal process phosphoric acid production (TPPAP) and wet process phosphoric acid production (WPPAP). TPPAP mainly involves heating using an electric donkey, blast furnace or kiln to reduce PR levels to obtain yellow phosphorus (YP) and then producing P2O5 through YP combustion. Finally, hydration creates phosphoric acid (PA). TPPAP is advantageous because resulting PA purity levels are high and fewer impurities are left. However, high levels of energy are consumed in the development of a unit product, and tail gas emissions generate considerable levels of environmental pollution. The WPPAP mainly involves using sulfuric acid and other inorganic acids to decompose PR into PA and then further purification using a variety of phosphorus chemical products (Afshar et al., 2003). The energy consumption of WPPAP is approximately equal to that of TPPAP at 35%. The method is advantageous in terms of environmental protection and cost efficiency (Afshar et al., 2003). However, resulting product quality levels are not high (containing impurities Fe, Al, Mg, F, Si and S) and purification is required (Monser et al., 1999). Mining and processing processes also generate considerable waste emissions (including solid waste and exhaust gas), leading to environmental pollution. Therefore, the phosphorus resources industry chain is mainly related to resources, industries, the economy, and environment subsystems under traditional modes. The traditional phosphorus resources industry chain is based on the

The development of the phosphorus resource industry faces serious challenges. It is thus necessary to re-examine difficulties faced from a comprehensive perspective and to conceptualize future development from a higher starting point. To break through the current development bottleneck, it is necessary to analyze the development and utilization of phosphorus resources in consideration of resources, industries, the environment, society, and so on in a comprehensive and systematic way. Phosphorus resources industrial system modeling is a complex problem due to the presence of multiple decision makers, complexity of suppliers and consumers’ behaviors, feedback processes among module, technological limitations and various kinds of delays. System dynamics (SD) is a suitable approach to model such complexities. SD is a powerful methodology and modeling technique for understanding and exploring the feedback structure in complex systems. It is based on systems and feedback control theories, computer simulation technologies, simulation study system feedback structures, behaviors and discipline functions (Forrester, 1971). SD involves both qualitative analysis and quantitative expression, focusing on the overall feedback structure of a system. It is suitable for dealing with high-order, multivariable, nonlinear and complex time-varying system problems. It is possible to find the best solution to a problem by simulating system 187

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Fig. 1. Analysis of phosphorus resources industry processes, including resource, industrial, economic, environmental and social subsystems.

key variables in the model, with a positive (+) or negative (−) sign placed beside the arrowhead, representing the relationship between variables (Ford, 1999). The entire SD model in our study considers economic, resource, environmental, industrial and societal subsystems with a variety of positive and negative feedback structures via the introduction of market regulation, environmental constraints, government support, social innovation and industrial transformation mechanisms (Ma et al., 2015a) (Fig. 2a shows the main relationships of the five subsystems, Fig. 2b shows the detailed feedback loops). The main feedback loops between these five subsystems are identified as follows. With the increase in the amount of PR mining (Resource), phosphorus industry capacity will expand, such as the production of PF, PA, YP will increased (Industry). Capacity expansion, on the one hand, it will promote economic development (Economy), on the other hand it also led to an increase in waste (i.e., solid waste and waste gas) emissions (Environment). Subsequently, environmental pollution leads to a decline in social satisfaction and government support (Society). Concurrently, due to environmental pressure, the investment in environmental protection needs to be increased, eventually leading to reduced net benefits. As a result, it will directly affect the next round of industrial expansion activities. Fig. 2b shows a circuit feedback loop with PF as an example (in bold lines of orange).

rich natural resources. However, extensive development has brought serious environmental pollution problems, including tailings pollution, phosphorus-containing waste and non-phosphorus waste emissions. At the same time, a single pursuit of production development mode led to a serious overcapacity of domestic phosphorus products, especially for the low-quality phosphorus products. Therefore, the transformation and upgrade of phosphorus resource industry is imminent. In order to solve the problems of tailings pollution, pollutant discharge in production process, overcapacity, low proportion of high value products and insufficient government supervision, and eventually realize the sustainable development of the phosphorus resources industry, this paper puts forward the transformation mode with the following key measures: 1) Tailings recovery and utilization for reducing environmental pollution (Ma et al., 2015b); 2) The gradual promotion of WPPAP as an alternative form of TPPAP (Afshar et al., 2003),adding new fertilizers and applying industrial-grade phosphoric acid downstream modules to increase the proportion of high value-added products (Ma et al., 2015b) which can reduce waste emissions while increasing the output value of phosphorus industry. 3) Introduction to market adjustments and elimination mechanisms to guide product structure adjustments that is useful to solve the problem of excess capacity; 4) The application of social subsystems and consideration of governmental policy support and constraints, financial capital support and technical assistance which is valuable for increase in environmental binding (Fang et al., 2007). These measures are shown by yellow blocks and the new material and information flows under the transformation mode is indicated by red line denotes in Fig. 1. By analysis of systematic structure to understand elements of the system and relationships among them, we have a clear understanding of the system boundary and find out the systematic characteristics and structures macroscopically.

2.2. Model development Numerous types of software programs and languages have been developed for constructing and testing SD models (Khaitan and McCalley, 2013). Vensim, ithink and Stella are commonly used SD software programs. In this study, we use the Vensim DSS 5.11, a software program (Ventana Systems, Inc., 2012), which integrates systems thinking, model building, behavior simulations, system optimization and variable analysis techniques. It can better examine causal relationships among variables and can demonstrate the dynamic evolution processes of a system. As CLDs cannot be used to manage variable accumulation and system responses, Stock and Flow Diagrams (SFDs) are used to

2.1.2. Generalized interactions among subsystems Based on the above structures analysis, we can establish flow diagram to further describe logical structure of the system which named Causal Loop Diagram (CLD). The CLD shows the feedback loops among 188

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Fig. 2. SD model of the phosphorus resources industry. (a) The main relationships among the five subsystems. (b) The detailed CLD of the phosphorus resources industry.

chemicals industry, key WPPAP and TPPAP technologies have gradually taken a leading position in China (Ma et al., 2015b). Therefore, Guizhou can represent the development of China's WPPAP and TPPAP technology.

represent the quantitative relationships between system variables and to measure system responses at any given moment (Sokolowski and Banks, 2009). Our detailed causal analysis and simplified SFDs (Fig. S214) and the functional relationships (Table S1-5) of each subsystem are shown in the Appendix Section. The definitions, units, type of the variable are also shown in Table S1-5. The data sources of variables and parameters of SD model are described in detail in Section 3.

3.2. Data sources The operating time range of the SD model of phosphorus resource industry evolution in Guizhou Province is set to 20 years from 2005 to 2025, of which 2005–2013 is historical data (Table S6-11). We set 2014 as the starting year of the transformation mode. Historical data were largely collected from the following sources. 1) National and provincial statistical databases, including “China Statistical Yearbook 2006–2014,” “China Mining Yearbook 2006–2014,” “China Statistical Yearbook on Environment 2006–2014,” “China Chemical Industry Statistical Yearbook 2006–2014,” “Guizhou Statistical Yearbook 2006–2014,” “Guizhou Yearbook 2006–2014,” and “Fuquan Yearbook 2006–2014”; 2) the China Phosphate Fertilizer Industry Association and 3) network public data. Relevant conversion and technical parameters were drawn from phosphorus chemical-related research results and methodologies and from local economic and technical indicators. Time-dependent parameters were extrapolated according to historical and actual trends (i.e.,

3. Case study: phosphorous resource industry in Guizhou Province, China 3.1. Study area Guizhou Province is located in the southwestern region of China (Fig. 3). Since the discovery of PR in 1955, Guizhou Province has served as a key phosphorus chemical resource base in China based on mining, dressing and processing (Ma et al., 2015b). At present, Guizhou Province is the most important production base for PF, YP and phosphate in China. The histograms in Fig. 3 represent PR production, phosphorus chemical industry sales, YP production and PF production in China and Guizhou in 2014 (Ren and Zhong, 2014; Sheng, 2014). These four indicators accounted for 28.31%, 23.90%, 10% and 18% of the country’s overall values, respectively. With the development of the phosphorus 189

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Fig. 3. Location of Guizhou Province in China and the development of the phosphorus chemicals industry.

4. Results and analysis

mining growth rates, exploration growth rates, resource and environmental impact coefficients, product growth rates of downstream phosphoric acid, new fertilizer growth rates, etc.). Various production and processing factors, costs, and so on are based on specific project estimates (National Science & Technology Pillar Program during the twelfth five-year planning period; Project Code: 2011BAC06B01; Project commitment unit: Wengfu Group Co., Ltd.). A detailed description of the parameter values is given in the Appendix (Table S12).

4.1. Model validation and sensitivity analysis 4.1.1. Model validation According to characteristics of the SD model of industrial systems of phosphorus resources, we select variables with complete historical data for 2005–2013 as our object of inspection to investigate the consistency of simulation results and historical data. In the model validation, we used two variables, PR production and YP production, to compare with historical data. The simulation results show that the relative error of PR production ranges at ± 4.00% (Fig.S15a) and that the value for YP production falls between −5.00% and −1.00% (Fig.S15b). This means that the historical and simulated values of the model variables are basically the same and that the relative error is small enough and thus meets prediction requirements and can be used for subsequent analyses. Therefore, the model is considered valid.

3.3. Variable definitions Based on the centrality analysis of variables in the SFDs, the number of equations involved and the causal analysis of the subsystems, representative variables are selected to characterize the future development of each subsystem under the two modes (Table 1).

4.1.2. Sensitivity analysis Sensitivity analysis is designed to determine the impact of selected variables on the operational structure of the model by change of important variables of a model within a certain range and analysis of changes in model output variables (Liu et al., 2015a). Here, environmental protection investment ratio of WPPAP and investment utilization coefficient are chosen to conduct sensitivity analysis. As is shown in Fig. S16, the total output value of the WPPAP industry and the total output value of the phosphorus resources industry after 2015 should change slightly with changes in the environmental proportion. This can be attributed to the fact that the proportion of environmental change should directly affect the output value of nonphosphorus products, thereby affecting the total output value of the WPPAP industry and the total output value of the phosphorus resources industry. However, the output value of non-phosphorus products from the proportion of the total output value is small, and so the sensitivity

Table 1 Representative variables of each subsystem. Subsystem

Representative variables

Resource subsystem

PR mining, dressing, consumption and output Resources and environmental carrying capacity Annual production of fertilizers Annual production of phosphorus products Total output value of phosphorus resources Cumulative emissions of pollutants Annual emissions of pollutants Public satisfaction Policy constraint index and policy support index Resource productivity Ecological efficiency

Industrial subsystem Economic subsystem Environmental subsystem Social subsystem General analysis

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environmental capacity of Guizhou Province will be unable to maintain resource mining activities and current rates of environmental destruction after 2025. In contrast, under the transformation mode, the decline in the resources and environment carrying capacity is greatly reduced. By 2025, the resources and environment carrying capacity will reach 229.29 Mt, which is equivalent to values found for roughly 2023 under the traditional mode. Therefore, to improve resources and environment carrying capacity levels, it is necessary to boost the recovery of tailings.

analysis does not show a considerable response which is in accordance with the expected results of the model mechanism. Similarly, the sensitivity analysis of investment utilization coefficient also conforms to the expected model mechanism analysis. Investment utilization coefficient will directly affect the pollutant handling capacity, here we take investment utilization coefficient of phosphogypsum as an example (Fig. S17a). Changes in investment utilization coefficient will inevitably lead to changes in the amount of phosphogypsum treatment, thereby affecting the corresponding changes in non-phosphorus product yield, resulting in non-phosphorus product output changes (Fig. S17b). While the cumulative storage of phosphogypsum depends on the difference between the amount of production and treatment, so the change in the amount of treatment does not directly affect the cumulative storage (Fig. S17c). Changes in public satisfaction are subject to changes in all the cumulative discharge of pollutants in WPPAP and TPPAP, so a single change in phosphogypsum will just slightly affect public satisfaction (Fig. S17d). Therefore, the sensitivity analysis shows that the model is sound and can be applied to additional strategy simulations.

4.2.2. Industrial subsystem 4.2.2.1. Analysis of PR consumption and service life values. As PR is a non-renewable resource, the service life is an important parameter for assessing the sustainable development of phosphorus resources. The base reserves of PR in Guizhou Province in 2011 is 528 Mt. According to the PR consumption rate under traditional mode, the cumulative consumption of PR in 2042 will reach the basic reserve value (According to binomial predictions, R2 = 0.9998). On the other hand, the cumulative consumption of PR will reach the base reserve value in 2073 under the transformation mode (According to binomial predictions, R2 = 0.9992). If we set the 2011 as a zero point, the service life under the traditional and transformation modes are 31 and 62 years, respectively (Fig. 5). In contrast, the service life of PR can be extended by 31 years under the transformation mode, which means production pattern changes and product structure adjustments of the phosphate resources industry under the transformation mode plays a significant role in saving PR resources.

4.2. Comparative analysis of traditional and transformation modes 4.2.1. Resource subsystem 4.2.1.1. PR mining, dressing and output analysis. The exploitation and processing of PR has a profound impact on the sustainable development of phosphorus resources. Under the traditional mode, the annual PR mining growth rate reached 9% in 2014 (Fig. 4a). After 2014, the mining growth rate began to decline, but this decline slowed to more than 1%. If PR production continues at the current speed, PR mining and dressing will continue to increase. After 2020, PR exploration will reach 40 Mt/yr. By 2025, PR mining volumes will reach 42.61 Mt and beneficiation levels will reach 340,900 tons. Compared to that of the traditional mode, the PR mining growth rate decreases under the transformation mode. By 2025, PR mining and dressing will reach 294,900 tons and 235,900 tons, with declines of 30.79% and 30.8% relative to values of the traditional mode, respectively. Through the long-term control of upstream mining speeds, forecasted PR mining levels will reach an inflection point in 2017 or 2018 as is shown in Fig. 4a. After regional consumption levels are reached, excess PR will be exported to the other region. PR outputs under the traditional and transformation modes show a completely different trend (Fig. 4a). PR output levels have been increasing under the traditional mode, as the increase in PR mining and dressing is far greater than that of the phosphate chemical industry in the region in regard to phosphate consumption demand. By 2020 and 2025, PR outputs will reach 16.17 Mt and 18.33 Mt, respectively. Under the transformation mode, PR output levels will increase first, and a peak value will appear in 2017 followed by a yearly decrease. This can be attributed to lower consumption levels under the transformation mode alongside production volumes that still show an inertial increase. However, PR mining and dressing will gradually adjust under the transformation mode, and final outputs also show a downward trend.

4.2.2.2. Analysis of phosphorus product production levels. In view of the total production of PF control, high-concentration phosphate fertilizer (HCPF) as a main variety of PF accounts for more than 85% of the total. Therefore, through the market phase-out mechanism, controlling the production of HCPF constitutes a main reason for transformation and upgrading. As is shown in Fig. 6a, the HCPF will continue to increase under the traditional mode, exceeding 20 Mt in 2017 and 3.26 Mt in 2025, and the output of PF is not decreased as a result. In contrast, for the PF control policy, the expected output of the HCPF decreases significantly from 2.65 Mt in 2014–1.98 Mt in 2017 with ideal type characteristics. However, under the transformation mode, HCPF production as simulated by the model should slowly decrease after 2014 and eventually reach a new equilibrium of roughly 1.65 Mt by 2021. Other phosphorus-containing products mainly include low-concentration phosphate fertilizer (LCPF), PA and YP. As is shown in Fig. 6b, the LCPF of both modes shows a trend of continuous decline in line with current development trends of realistic systems. However, due to the unique characteristics of the LCPF (e.g., calcium PF as a typical alkaline fertilizer for acidic soils in southern China and HCPF surplus soil), the LCPF also shows room for development, and the species will be improved and occupy a certain market share. Compared to that of the traditional mode, the rate of decline of the LCPF under the transformation mode is relatively slow at 52.6% from 2014 to 2025, which is 16.4% higher than that of the traditional mode. These results are in line with expectations for LCPF industry development. YP product output levels remain stable overall with a slight increase, denoting that over the next 10 years, the industry will undergo steady development. For PA products, under the traditional mode, outputs will first increase rapidly and then rise gently. Regarding the current PF surplus, if rapid increases, such as those of recent years, are maintained, a new surplus crisis will result. Thus, under the transformation mode, phosphate products are expected to show a gradual increase early on and then a steady rise. In approximately 2020, as downstream demand for high-end phosphate products increases and with WPPAP purification technology breakthroughs, PA production will increase further. Fig. 6c shows the proportions of PF (including HCPF and LCPF), PA

4.2.1.2. Analysis of resources and environmental carrying capacities. Resources and environmental carrying capacities reflect the extent of effects of PR mining processes on the environment (equation shown in table S1). In 2011, the resources and environment carrying capacity reached a peak of 890.36 Mt (Fig. 4b). From a decrease in the annual exploration volume, an increase in the annual mining volume and an increase in the environmental binding force, the carrying capacity of resources and the environment will be reduced. However, under different development modes, the degree of resource carrying capacity decline varies. Under the traditional mode, the resources and environment carrying capacity will drop to 405.3 Mt by 2020 and to −12.61 Mt by 2025, which shows the resources and 191

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Fig. 4. Comparison and analysis of resource subsystem simulation results under two modes. (a) PR mining, dressing, consumption and output; (b) Resources and environment carrying capacity levels.

Fig. 5. Accumulated consumption and service life values for PR under two modes.

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Fig. 6. Analysis of phosphorus product production. (a) The change trend of HCPF production under two modes; (b) The change trend of LCPF, PA and YP production under two modes; (c) Proportions of PF, PA and YP under the transformation mode; (d) For the transformation mode, a comparison of downstream phosphoric acid consumption levels for 2014 and 2025.

process will be accompanied by non-phosphorus products. If the companion is not treated and used, it will be converted into pollutants discharged into the environment, thus destroying the ecological environment. In protecting the environment, government investments will result in a certain degree of economic loss, and mainly in terms of sewage charges, safe disposal costs, and ecological compensation. To further describe the impacts of environmental costs, we examine the impact of pollutants on our economic variables to objectively reflect on the impact of pollutant emissions on economic losses. The total output value of the phosphorus resources industry generally includes the total output value of the TPPAP and WPPAP industries. With this concept, we consider non-phosphorus products and economic losses, and the four types of output are classified as follows: non-phosphorus output value and economic loss (NPEL), non-phosphorus output value without economic loss (NPNEL), economic loss without non-phosphorus output value (NNPEL), and without nonphosphorus output and economic loss (NNPNEL). Under the traditional mode, the total output value of the phosphorus resources industry for 2014–2025 shows an upward trend (Fig. 7a). The four types of output value in descending are as follows: NPNEL > NNPEL > > NPEL > NPNEL. Overtime, this trend becomes more pronounced. The value without economic loss (NPNEL and NNPNEL) was found to be significantly higher than that with economic loss (NPEL and NNPEL). This denotes that for pollutants that cause economic damage under this mode, the output value of non-phosphorus products cannot make up for losses. This gap becomes more pronounced overtime, suggesting that ecological damage resulting from

and YP for the transformation mode. The proportion of PF will be gradually reduced from 78.3% in 2014–56.5% in 2025, PA will increase from 14.5% to 26.6%, and YP will increase from 7.2% to 16.8%. Fig. 6d shows the allocation of fine phosphates downstream from WPPAP under the transformation mode. From the purification of downstream products through WPPAP, total PA consumption should reach 356,000 tons in 2014 and 804,000 tons in 2025. The most consumed varieties are generated for the production of feed followed by fine phosphates, flame retardants, high value-added phosphates and lithium iron phosphates. Compared to 2014 values, the ratio of calcium is reduced and the proportion of lithium iron phosphate is increased, indicating that through product design and production technologies, product variety levels can be converted, thus adjusting the direction of the phosphorus flow and resource allocation ratio. The application of transformation measures that optimize the downstream product structure of phosphate contributes to the improvement of resource output efficiency levels. The simulation results show that the resource productivity of lithium iron phosphate reaches nearly 290,000 yuan/ton (Table S13), proving that this method generates higher added value and thus that its proportion increases rapidly through the optimization process. According to changes in and requirements of the downstream demand structure, the product structure has been further optimized and adjusted, promoting the healthy development of the industry and effectively increasing the added value of products. 4.2.3. Economic subsystem Phosphorus-containing products generated through the production 193

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Fig. 7. Analysis of output values of the phosphorus resources industry. (a) Total output value of phosphorus resources under the traditional mode; (b) Total output value of phosphorus resources under the transformation mode.

respective two modes. Annual pollutant discharge is a key parameter that reflects the annual dynamic change in industrial pollutant levels. As is shown in Fig. 8b, the annual discharge of pollutants in 2014 was 16.4 Mt under the traditional mode and 16.1 Mt under the transformation mode, respectively, representing a minor difference. Since 2014, due to product output changes, pollutant discharge under the traditional mode has increased to more than 20 Mt continuously while under the transformation mode, total discharge first showed a significant decrease and then a smaller-amplitude rebound with an overall control value of 15 Mt or less. This is attributed to the internal structure of industrial restructuring and to the fact that the balance mechanism of market demand has led to a decline in production. Therefore, the annual discharge of pollutants has also decreased. However, cumulative discharge under the transformation mode is still increasing. Pollutant utilization methods have not been greatly improved. Under the latter part of the transformation mode, there will be a further increase in pollutant levels. Therefore, to improve the efficiency of resource utilization mechanisms and to mitigate environmental impacts, we must encourage the recycling of pollutants by advanced technologies.

the development of this industry will be aggravated, thus hindering the sustainable development of this industry. Under the transformation mode, the total output value of the phosphorus resources industry for 2014–2025 first decreases and then increases (Fig. 7b). From 2014–2021, NPNEL was found to be slightly larger than NNPNEL, NPEL and NNPEL values. However, from 2020 to 2025, NPNEL values are first slightly larger than NPEL values and are then slightly larger than NNPNEL and NNPEL values later on. Overall, the output value of non-phosphorus products is slightly higher than that of products not containing non-phosphorus under the transformation mode. This indicates that the output value brought about by nonphosphorus products is greater than the value of pollutant damages to the economy. The essence of this result is equivalent to non-phosphorus output and economic losses of the game. In early stages of the transformation mode, the impact of economic losses is still dominant. However, after 2021, non-phosphorus products offset the profits of economic vacancies and the economy to a certain level of compensation, and resulting advantages become more and more obvious and ultimately begin to dominate. On the basis of NPEL, if we consider the economic benefits of agricultural services (AS), the resulting value is much higher than that achieved under other conditions. The treatment of non-phosphorus waste can not only reduce environmental pollution, but also increase the production of corresponding non-phosphorus products, thereby increasing the output value of the phosphorus chemicals industry. In such cases involving a certain level of waste discharge, the production of non-phosphorus products and the use of pollutants is consistent with the treatment and emission of pollutants according to the opposite trend.

4.2.5. Social subsystem Policy support and environment restraint mechanisms of the social subsystem play a balanced role in the entire social subsystem, and the subsystem is regulated by support and constraint index changes. Both the policy constraint index and policy support index tend toward 1 (Fig.S18). Until 2017, the role of policy constraints has dominated, but with the implementation of innovative measures under the transformation mode, the role of policy support has gradually become more central. Public satisfaction, as an important index of social subsystem feedback to the industry subsystem, reflects the production process while taking into account effects on the environmental and social subsystems (definition and equation are shown in Section 3.5 of the appendix). According to the structure of the SD model, public satisfaction directly affects the economic impacts of pollutant discharge and the proportion of investment dedicated to environmental governance. The reduction in pollutant emission increases public satisfaction from 2.0 in 2014–3.1 in 2025 under the transformation mode (Fig. 9). From this causal relationship, it can be concluded that public satisfaction and annual pollutants discharge follow opposing trends. Therefore, the improvement in pollutant control is an effective way to improve social satisfaction.

4.2.4. Environmental subsystem The cumulative discharge of pollutants is composed of pollutant discharge through WPPAP and TPPAP. The cumulative amount of pollutant discharge increases with time. However, the cumulative increase in pollutant levels under the transformation mode is less than that of the traditional mode, and the gap between the two modes is increasing (Fig. 8a). As is shown in Fig. 8a, the cumulative discharge of pollutants through WPPAP and TPPAP for 2020 under the transformation mode reaches 180.9 Mt, which is less than the 184.7 Mt level of cumulative discharge from WPPAP under the traditional mode. By 2025, the total amount of cumulative discharge from the transformation mode will account for 76.3% of that of the traditional mode. Under the same mode, pollutant discharge from WPPAP is much greater than that of TPPAP. The proportion discharge from WPPAP increases from 79.8% and 79.7% in 2014–89.6% and 86.1% in 2025 under the 194

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Fig. 8. Analysis of pollutant discharge trends under two modes. (a) Cumulative discharge of pollutants; (b) Annual discharge of pollutants.

transformation mode fluctuates as a whole and shows a slow upward trend. Therefore, when the denominator of the resource yield rate does not change significantly, when the number of molecular items can be increased (e.g., through the extension of the producer responsibility system, through the use of pollutant reduction and clean-up measures for reducing losses, via profits created through the reuse of waste, agricultural services and the use of new environmentally friendly fertilizers for additional benefits, etc.), resource productivity levels can be increased.

4.3. Comprehensive comparative analysis 4.3.1. Analysis of resource productivity Resource productivity is calculated as follows: Resource Productivity = Total output value of phosphorus resources/PR consumption, as a comprehensive indicator that reflects resource consumption and output value through a coordinated relationship whereby the greater the index value, the greater the output of resources per unit (Boudreau, 1983). For the molecular term, the type of output value contains the NPEL. Under the traditional mode, the resource productivity of WPPAP increases slowly. However, the resource productivity of TPPAP tends to decrease, and resource productivity levels decrease to 119.4 yuan/ton in 2021 and −27.6 yuan/ton in 2022 (Fig. 10a). This is mainly attributed to the fact that the total output value of TPPAP is negative, and the impact of pollutants on the economy exceeds the sum of the output value of phosphorus and nonphosphorus products. Rather, under the traditional mode, environmental pollution should cost more than industrial outputs in the future. In contrast, the resource productivity of WPPAP and TPPAP under the

4.3.2. Analysis of ecological efficiency levels Ecological efficiency is calculated as follows: Ecological Efficiency = Total output value of phosphorus resources industry/Total pollutant discharge., as a comprehensive indicator that reflects the coordinated relationship between pollutant discharge and production value (Hockerts, 1999). The larger the indicator, the greater the output value of the pollutant unit becomes at the expense of emissions. Like resource productivity, measures for increasing the output value of phosphorus resources and for reducing pollutant emissions can improve Fig. 9. Public satisfaction under two modes.

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Fig. 10. Comprehensive comparative analysis based on two modes. (a) Resource productivity; (b) ecological efficiency.

promoted. To boost ecological efficiency, the utilization of waste resources should be encouraged through industrial development. 4) Tax and subsidy policies should be reformed, sewage charges on polluting enterprises should be imposed, and tax incentives and subsidies for environmental protection enterprises should be created. The government should act as the market to guide business investment. 5) The convergence of production and application should be promoted to achieve product and service integration, and especially in the fertilizer industry.

ecological efficiency levels. In Fig. 10b, the ecological efficiency of the transformation mode increases from 1391 yuan/ton in 2014–2153 yuan/ton in 2015 (an increase of 55%) while ecological efficiency under the traditional mode fluctuates at roughly 1000 yuan/ton. In essence, pollutant recycling, by improving resource utilization, can effectively improve ecological efficiency levels. 5. Conclusions and suggestions The sustainable development of the phosphorus resources industry has received extensive attention. The reliable system simulation of its entire industrial system is critical to the sustainable development of this industry. As SD models can be used to examine dynamic feedback relationships within a system, in this study, an integrated SD model was developed to identify issues that must be addressed in industrial development and to suggest pathways for transformation and upgrading. Based on traditional industrial processes and bottlenecks affecting the development of the phosphorus resources industry, we focus on mechanisms of market regulation and elimination, government support and environmental constraint and on the feedback structure between social innovation and industrial production systems. We then put forward a means of developing the transformation mode. The results show that the service life of PR can be extended by 31 years. By 2025, resource productivity and ecological efficiency levels should increase to over twice those of 2014. In addition, social satisfaction levels should increase by roughly 50% under the transformation mode. Based on our analysis, the following five suggestions are proposed in regard to the development of the phosphorus resources industry in China.

This study presents a pathway for the sustainable development of phosphorus resources at meso level that complements research on macro and micro factors and that complements the perspective of industrial evolution. These simulations can help assess the effects of various policies and provide support for decision making in sustainable development of phosphorus resources and environmental management. Based on the requirements of economic and industrial sustainable development, it can also be applied in other non-fossil resource management research and provide useful insights for the relevant industries which are facing the transformation and upgrading. Acknowledgments This study was supported by the National Science & Technology Pillar Program during the twelfth five-year planning period (Project Code: 2011BAC06B01), National Natural Science Foundation of China (Project Code: L1522024) and Chinese Academy of Engineering (Project Code: 2015-ZCQ-009). We also wish to express our gratitude to the Wengfu Group.

1) Under government regulation, a market orientation should be gradually encouraged and the balance between the market and government should be strengthened. Through market adjustments and elimination mechanisms, backward production capacity should be gradually eliminated and corporate restructuring and mergers should be supported to reverse overcapacity phenomena. 2) Product structures should be transformed, and the proportion of phosphate fertilizer products should be reduced, and the proportion of high value-added products (e.g., high-end phosphates, electronic grade phosphoric acid products, fine phosphorus products and new phosphate fertilizers) should be increased. Resource productivity should be improved through the promotion of new technologies. 3) Awareness of environment protection standards should be enhanced, pollution emitted under corporate governance should be standardized, and the utilization of waste resources should be

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