K 2 MgSi 3 O 8 in Slow-Release Mineral Fertilizer Prepared by Sintering of By-Product of Red Mud-Based Flocculant

Abstract

Because of the large amounts of iron and aluminum in red mud, which is a by-product of the alumina industry, aluminum and iron can be extracted by HCl or H₂SO₄ to produce inorganic flocculants. However, residues produced by acid leaching pose environmental problems. In this study, a slow-release mineral fertilizer K₂MgSi₃O₈ is prepared at 1,000°C for 2 h by sintering the flocculant by-product based on red mud. The main mineral in the fertilizer is K₂MgSi₃O₈, with an irregular blocky morphology. In distilled water, 0.50 mol/L HCl, and 20 g/L citric acid, the dissolution rates of K₂O are 13.13%, 96.36%, and 81.46% and those of MgO are 2.03%, 70.94%, and 66.03%, respectively. Cumulative release values of K₂O and MgO are 6.98% and 0.01% on the first day and 56.12% and 1.70% after 28 days, and the slow-release rates satisfy the Chinese standard for slow-release fertilizers. Hence, the mineral fertilizer K₂MgSi₃O₈ based on the by-product of red mud is a potential slow-release fertilizer.

Introduction

The world population is projected to reach 9.2 billion in 2075 according to the World Bank, thus placing increasing demands for food; however, the amount of usable land for agriculture is diminishing due to housing and industrial necessities (Adachi and Patel, 1999; Wasilewski and Krukowski, 2004). High food productivity is, thus, crucial, and crop yields can be boosted by using fertilizers (Ghosh et al., 2004). However, the efficiency of many fertilizers is not good because of the high solubility of chemical fertilizers and plants cannot absorb them in a timely manner. In addition, the soluble entities may contaminate ground water and deteriorate the soil structure (Adetunji, 1994), but these drawbacks can be circumvented with slow-release fertilizers (Xie et al., 2011; Hazra and Das, 2014; Haynes, 2014). Recently, slow-release mineral potassium-based fertilizers have been studied as a source of potassium for crops, for example, fused potassium silicate K₂Ca₂Si₂O₇ (Arroyabe and Kahlenberg, 2011; Yao et al., 2014), potassium silicate, K₂MgSiO₄, K₂MgSi₃O₈ (Tokunaga, 1991; Pérez et al., 1999), zeolite-based fertilizers such as phillipsite and merlinoite (Pino et al., 1995; Li et al., 2014), as well as mechanochemically formed fertilizers such as K-Si-Ca-O (Zhang et al., 2009; Solihin et al., 2010, 2011; Yuan et al., 2014) and KMgPO₄ (Tomaszewski et al., 2005). K₂MgSi₃O₈ has a structure similar to that of KAlSiO₄, which is known as natural or synthetic kalsilite or kaliophilite (Ma et al., 2014, 2016; Su et al., 2014). It can be used as a slow-release potassium silicate fertilizer to provide K, Mg, and Si to crops. K₂MgSi₃O₈ is prepared with fly ash, molten ash, oil-shale residues, lime shale, and rice husks (Tokunaga, 1991; Pérez et al., 1999; Mangrich et al., 2001).

Red mud is the waste product of caustic digestion of bauxite during extraction of alumina. For every ton of alumina produced, approximately one to two tons (dry weight) of bauxite residues are generated. The corrosive nature of red mud and large quantities (90 million tons yearly worldwide) cause significant ecological and environmental problems. Red mud is rich in iron and aluminum, which can be extracted HCl or H₂SO₄ to produce inorganic flocculant (Lu et al., 2011, 2014; Wang et al., 2014). Although the residues from red mud produced by acid leaching pose environmental problems, they are potential raw materials for the slow-release mineral fertilizer K₂MgSi₃O₈. In this study, K₂MgSi₃O₈ is prepared with the acid-leached residues from red mud, brucite, and K₂CO₃ by solid-phase sintering and the solubility and slow-release properties are investigated systematically.

Experimental Details

Materials

The red mud was provided by Shandong Weiqiao Aluminum and Electricity Co., Ltd. (Shandong, China). The polymeric aluminum iron flocculant was prepared with the red mud and 27% industrial waste HCl by Shandong Jingtai Co., Ltd. The production flow chart is shown in Fig. 1. The filtrate was the raw liquid of the flocculant. The acid-leached residue was washed with 500 mL water three times to obtain the raw materials as the silicon source. The acid-leached residue of red mud was designated as ALR. Brucite was supplied by Kuandian Brucite Factory (Liaoning, China), and the main chemical composition is listed in Table 1. The other reagents in this study were of analytical grade.

FIG. 1.

Production flow chart of acid-leached residue of red mud.

Table 1.

Chemical Composition of ALR and Brucite

Chemical composition	SiO₂	Al₂O₃	CaO	Fe₂O₃	TiO₂	K₂O	MgO	Cl	Na₂O	P₂O₅	Loss
ALR	40.63	20.10	1.47	9.90	9.18	0.28	0.25	1.87	0.33	0.48	15.01
Brucite	8.27	0.12	1.21	0.18		0.01	61.21				28.85

ALR, acid-leached residue of red mud.

Preparation of K₂MgSi₃O₈ mineral fertilizer

ALR, brucite, and K₂CO₃ (the mass ratio 6.53:1.00:2.10) were mixed with the stoichiometric ratio of K₂MgSi₃O₈ and placed in an alumina crucible. The sintering reaction proceeded in a muffle furnace (Ajeon Heating Industrial Co., Korea). The synthesis flow chart of K₂MgSi₃O₈ mineral fertilizer using ALR, brucite, and K₂CO₃ is shown in Fig. 2. To determine the optimal conditions, the sintering temperature was studied based on thermogravimetric (TG) data of the mixture of ALR, brucite, and K₂CO₃. The optimal sample was designated RMF. The main reaction is as follows: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} \begin{split} 3{ \rm{Si}}{{ \rm{O}}_{ \rm{2}}} \left( {{{ \rm amorphous}}} \right)+{ \rm{Mg}}{ \left( {{ \rm{OH}}} \right) _2} + {{ \rm{K}}_2}{ \rm{C}}{{ \rm{O}}_3} \; \\= \;{{ \rm{K}}_2}{ \rm{MgS}}{{ \rm{i}}_3}{{ \rm{O}}_8} + { \rm{ C}}{{ \rm{O}}_2} \uparrow + {{ \rm{H}}_2}{ \rm{O}} \uparrow\end{split} \tag{1}\end{align*} \end{document}

FIG. 2.

Synthesis flow chart of K₂MgSi₃O₈ mineral fertilizer using ALR, brucite, and K₂CO₃.

Characterization

Chemical composition and mineral components of ALR, brucite, and mineral fertilizer samples were determined by X-ray fluorescence (XRF) and X-ray diffraction (XRD). Thermal decomposition of the mixture of ALR, brucite, and K₂CO₃ was monitored by TG differential thermal analysis. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy, and N₂ adsorption were performed to characterize the structure and morphology of the samples.

Solubility and release properties

Solubility of the samples was measured according to the protocols of the Chinese chemical industry standard of calcium magnesium potassium phosphate fertilizers (HG 2598-94), the Chinese agricultural standard of soil amendment—Determination of calcium, magnesium, and silicon content (NY/T 2272-2012), and soil amendment—Determination of phosphorus and potassium content (NY/T 2273-2012). One hundred fifty milliliters of 0.50 mol/L HCl and 20 g/L citric acid (28–30°C) were added, respectively, to a 250 mL volumetric flask, which was shaken in a digital water bath oscillator for 80 min at 180 rpm. The sample was filtered; the concentrations of K, Mg, and Si in the filtrate were determined measured by inductively coupled plasma optical emission spectroscopy (ICP-OES); and the content of K₂O, MgO, and SiO₂ can be got by further calculation.

The nutrient release was investigated according to the Chinese national standard of slow-release fertilizer protocol (GB 23348-2009). Ten gram of the sample was put in a nylon mesh bag, added to 200 mL of distilled water in a 250 mL volumetric flask, and held at 25°C in the biochemical incubator. It was filtered after 24 h and at 3, 5, 7, 10, 14, 28, 42, 56, and 84 days. The concentrations of K, Mg, and Si in the filtrate were also determined measured by ICP-OES and the contents of K₂O, MgO, and SiO₂ are further calculated.

Results and Discussion

Preparation of RMF

The TG curve of the mixture of ALR, brucite, and K₂CO₃ is presented in Fig. 3. It reveals four weight losses of 8.64%, 3.04%, 5.85%, and 15.45% at 160°C, 257°C, 377°C, and 910°C, respectively. The first and second stages arise from elimination of physically adsorbed water and interlayer water. The third weight loss of 5.85% at 377°C is caused by decomposition of Mg(OH)₂ in brucite, and the fourth stage stems from the decomposition of K₂CO₃ and the crystallization of K₂MgSi₃O₈. The main weight loss is observed between 800°C and 1,000°C during which the RMF reaction occurs. Hence, sintering is performed between 800°C and 1,000°C for 2 h.

FIG. 3.

TG-DTG results of mixture of ALR, brucite, and K₂CO₃. TG-DTG, thermogravimetric-derivative thermogravimetry.

XRD patterns of the mineral fertilizers prepared at different sintering temperature for 2 h are depicted in Fig. 4. The main mineral phases in the mixture of ALR, brucite, and K₂CO₃ are anatase (TiO₂, PDF 21-1272), brucite [Mg(OH)₂, PDF 07-0239], and boehmite [AlO(OH), PDF 21-1307]. When the sintering temperature is 800°C, the main characteristic peak is anatase (TiO₂, PDF 21-1272), indicating that most of the materials are amorphous. The main characteristic peaks (21.03°, 27.7°, 28.76°, and 33.92°) of K₂MgSi₃O₈ (PDF 10-0030) begin to appear at a sintering temperature of 900°C, and the intensity increases with temperature from 900°C to 1,000°C (Ma et al., 2016). When the sintering temperature is 1,050°C, the peaks of the main by-product KAlO₂ (PDF 02-0897) appear and they are not conducive to the formation of the main mineral phase K₂MgSi₃O₈. Moreover, the higher is the temperature, the higher is the production cost. Therefore, 1,000°C is selected as the sintering temperature in subsequent experiments.

FIG. 4.

XRD patterns of mineral fertilizers prepared at different sintering temperature. XRD, X-ray diffraction.

Solubility of RMF

Chemical composition of RMF determined by XRF is shown in Table 2. The concentration of SiO₂, K₂O, and MgO is 36.55%, 20.33%, and 9.86%, respectively. The K:Mg:Si molar ratio of 1.76:1.00:2.49 is close to the theoretical ratio of K₂MgSi₃O₈ (2:1:3).

Table 2.

Chemical Composition of RMF

Chemical composition	SiO₂	K₂O	Al₂O₃	MgO	CaO	Fe₂O₃	TiO₂	Loss
wt%	36.55	20.33	15.53	8.86	5.17	4.41	4.12	5.44

The solubility of RMF in distilled water, 0.5 mol/L HCl, and 20 g/L citric acid solution is determined and the concentrations of K⁺, Mg²⁺, Si⁴⁺, Ca²⁺, and Al³⁺ in the filtrate measured by ICP-OES are summarized in Table 3. The solubility in HCl and citric acid is higher than that in distilled water, and the extracted concentrations of K₂O, MgO, SiO₂, and CaO in 0.50 mol/L HCl are larger than those in 20 g/L citric acid because the pH of 0.50 mol/L HCl (pH = 0.3) is smaller than that of 20 g/L citric acid (pH = 2.0), indicating that RMF is a citrate-soluble fertilizer with potentially desirable release properties. The weight losses (%) of RMF of 79.53% and 65.38% in 0.50 mol/L HCl and 20 g/L citric acid are larger than those in distilled water.

Table 3.

Solubility of RMF in Distilled Water, HCl, and Citric Acid

Solution	K₂O (g/L)	Dissolution rate (%)	MgO (g/L)	Dissolution rate (%)	CaO (g/L)	Dissolution rate (%)	SiO₂ (g/L)	Dissolution rate (%)	Al₂O₃ (g/L)	Dissolution rate (%)	Weight loss (%)
Distilled water	0.18	13.13	0.01	2.03	0.01	1.74	0.24	9.77	0.14	13.33	10.23
0.50 mol/L HCl	1.31	96.36	0.42	70.94	0.01	3.48	0.87	35.58	0.31	30.14	79.53
20 g/L citric acid	1.10	81.46	0.39	66.03	0.01	2.90	0.62	25.49	0.24	22.79	65.38

Characterization of RMF

XRD patterns of RMF and RMF in 0.50 mol/L HCl are shown in Fig. 5. After treatment in 0.50 mol/L HCl, the diffraction peaks of K₂MgSi₃O₈ and KAlSiO₄ disappear, suggesting that they dissolve or decompose in the solution. The XRD results of the residue in 0.50 mol/L HCl show that the main mineral phases are Fe₃Ti₃O₁₀ and Mg₂SiO₄ produced by the sintering process.

FIG. 5.

XRD patterns of (a) RMF and (b) RMF in 0.50 mol/L HCl.

The SEM images of the RMF and RMF in 0.50 mol/L HCl are displayed in Fig. 6. Figure 6a and b shows that RMF was smoother granular edge before treatment in 0.50 mol/L HCl (Fig. 6c, d). There were many holes on the surface of the RMF particles after the 0.50 mol/L HCl treatment, indicating that some of the particles dissolve. The surface area of RMF after the 0.50 mol/L HCl treatment increases from 45.40 to 73.40 m²/g and the porosity goes up from 4.00% to 13.00%, as shown in Table 4.

FIG. 6.

SEM images: (a, b) RMF and (c, d) RMF after treatment in 0.5 mol/L HCl. SEM, scanning electron microscopy.

Table 4.

Physical Properties of RMF and RMF After Treatment in 0.50 mol/L HCl

Samples	Particle size (μm)	BET (m²/g)	Bulk density (g/cm³)	Porosity (%)
RMF	30–120	45.40	4.10	4.00
RMF after HCl treatment	25–115	73.40	2.30	13.00

BET, specific surface area.

Release properties of RMF

In accordance with the Chinese national standard for slow-release fertilizers (GB 23348-2009), 10 g of RMF is put in a nylon mesh bag and added to 200 mL of distilled water in a 250 mL volumetric flask. At time points of 24 h as well as 3, 5, 7, 10, 14, and 28 days, the filtrates were analyzed by ICP-OES. The cumulative release amounts (%) of SiO₂ and K₂O are calculated based on Equation (2): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} {{ \rm Accumulative \ release }} \;\left( \% \right) = {c_i}V / m{ \rm{ }}{w_i} , \tag{2} \end{align*} \end{document}

where i stands for K₂O, MgO, SiO₂, CaO, and Al₂O₃; c_i (g/mL) is the concentration of component i in the filtrate; V is 250 mL; and m (g) and w_i (%) are the content of component I in the optimal sample. Fig. 7 shows that the cumulative releases of K₂O, SiO₂, MgO, and CaO are 6.98%, 3.44%, 0.01%, and 0.02%, respectively, on the first day and increase with time, reaching 56.12% K₂O, 38.18% SiO₂, 1.70% MgO, and 0.50% CaO, respectively, after 28 days. After 84 days, the cumulative releases reach 69.32% K₂O, 46.34% SiO₂, 4.40% MgO, and 0.73% CaO. The cumulative releases of K₂O and SiO₂ increase obviously but that of SiO₂ increases more slowly than K₂O. Conversely, the cumulative releases of MgO and CaO are close to equilibrium, with little release of MgO and CaO. The reason is that the solution of RMF is alkaline and Mg and Ca form precipitation. SiO₂ and K₂O in RMF dissolve in distilled water and the cumulative release is less than 80% after 28 days, thereby satisfying the Chinese national standard for slow-release fertilizers.

FIG. 7.

Cumulative release of K₂O, MgO, SiO₂, and CaO in RMF.

Heavy metal dissolution

Amounts of heavy metals in solid wastes affect the application. Table 5 shows the heavy metal concentration in RMF after 84 days in water and 0.5 mol/L HCl. The heavy metal contents are considerably smaller than the Chinese fertilizer standard. After 84 days in water, the concentrations of Hg, As, Cd, Pd, and Cr in the liquid are 0.0021, 2.045, 0.0032, 0.008, and 1.23 mg/kg, respectively, and the dissolution rates are 16.15%, 24.84%, 1.78%, 0.73%, and 5%, respectively. The dissolution rates of heavy metals are quite small and so, they do not affect crops.

Table 5.

Amounts of Heavy Metals in Comparison with Chinese Current Fertilizer Standard of Heavy Metals

Samples	Hg (mg/Kg)	As (mg/Kg)	Cd (mg/Kg)	Pb (mg/Kg)	Cr (mg/Kg)
RMF	0.013	8.32	0.18	1.09	24.6
GB/T 23349-2009	≤5	≤50	≤10	≤200	≤500
GB/T 18877-2009	≤5	≤50	≤10	≤150	≤500
NY/T 525-2012	≤2	≤15	≤3	≤50	≤150
Dissolution liquid of RMF after 84 days in water	0.0021	2.045	0.0032	0.008	1.23
Dissolution rate, %	16.15	24.84	1.78	0.73	5

Cost analysis

Total production cost of fertilizer is obtained in Table 6 by analyzing the raw material price and labor cost. The total cost of fertilizer of RMF is 1,554 CNY/t with available nutrient composition SiO₂ = 13.00%, CaO = 1.80%, MgO = 6.28%, and K₂O = 19.59%. However, the prices of calcium magnesium potassium fertilizer (SiO₂ ≥ 20.00%, CaO ≥20.00%, MgO ≥6.00%, K₂O ≥ 7.00%) and soil conditioner (SiO₂ ≥ 22.00%, CaO ≥23.00%, MgO ≥9.00%, K₂O ≥ 6.00%) in the market are 4,200 CNY/t and 4,000 CNY/t, respectively. The cost of RMF is much lower than that of calcium magnesium potassium fertilizer and soil conditioner in the market, and it has broad application prospects.

Table 6.

Economic Contrast Analysis Between RMF and Fertilizer with Equivalent Specifications

Raw material	Dosage (t)	Raw material price (CNY/t)	Cost (CNY)
ALR	0.68	50	34
Brucite	0.10	1,500	150
K₂CO₃	0.22	6,000	1,320
Labor cost (CNY/t)			50
Total production cost (CNY/t)	SiO₂ = 13.00%, CaO = 1.80%, MgO = 6.28%, K₂O = 19.59%		1,554
Calcium magnesium potassium fertilizer cost (CNY/t)	SiO₂ ≥ 20.00%, CaO ≥20.00%, MgO ≥6.00%, K₂O ≥ 7.00%		4,200
Soil conditioner cost (CNY/t)	SiO₂ ≥ 22.00%, CaO ≥23.00%, MgO ≥9.00%, K₂O ≥ 6.00%		4,000

Conclusion

The slow-release mineral fertilizer K₂MgSi₃O₈ is prepared with the acid-leached residue of red mud, brucite, and K₂CO₃ by solid-phase sintering at 1,000°C for 2 h. The mineral fertilizer is a citrate-soluble fertilizer and the extraction of K₂O, MgO, SiO₂, CaO, and Al₂O₃ in 0.50 mol/L HCl is larger than that in 20 g/L citric acid. The cumulative releases of K₂O and MgO are 6.98% and 0.01% on the first day and 56.12% and 1.70% after 28 days, indicating that the slow-release property satisfies the Chinese national standard of slow-release fertilizers. The dissolution rates of Hg, As, Cd, Pd, and Cr in 0.50 mol/L HCl are 0.0021, 2.045, 0.0032, 0.008, and 1.23 mg/kg, respectively, and indicate minimal influence on the quality of crops.

Compared with the mineral fertilizer in the market, the cost of RMF is much lower and indicates that it has broad application prospects.

Footnotes

Acknowledgments

This work was supported by the National Science-Technology Support Plan Projects [No. 2014BAC31B01], the National High Technology Research and Development Program of China [863 Program, No. 2012AA06A109], and the City University of Hong Kong Applied Research Grant (ARG) No. 9667122 and Strategic Research Grant (SRG) No. 7004644.

Author Disclosure Statement

No competing financial interests exist.

References

Adachi

, and Patel

(1999). Agricultural land conversion and inheritance tax in Japan. Rev. Urban Reg. Dev. Stud., 11, 127.

Adetunji

M.T.

(1994). Nitrogen application and underground water contamination in some agricultural soils of South Western Nigeria. Nutr. Cycling Agroecosyst., 37, 159.

Arroyabe

, and Kahlenberg

(2011). Structural investigations on the fertilizer component K₂Ca₂Si₂O₇. Eur. J. Mineral., 23, 101.

Ghosh

P.K.

, Ramesh

, Bandyopadhyay

K.K.

, Tripathi

A.K.

, Hati

K.M.

, Misra

A.K.

, and Acharya

C.L.

(2004). Comparative effectiveness of cattle manure, poultry manure, phosphocompost and fertilizer-NPK on three cropping systems in vertisols of semi-arid tropics. I. Crop yields and system performance. Bioresour. Technol., 95, 77.

Haynes

R.J.

(2014). A contemporary overview of silicon availability in agricultural soils. J. Plant Nutr. Soil Sci., 177, 831.

Hazra

, and Das

(2014). A review on controlled release advanced glassy fertilizer. Global J. Sci. Front. Res., 14, 32.

, Zhuang

, Font

, Moreno

, Vallejo

V.R.

, Querol

, and Tobias

(2014). Synthesis of merlinoite from Chinese coal fly ashes and its potential utilization as slow release K-fertilizer. J. Hazard. Mater., 265, 242.

G.L.

, Yu

H.Y.

, and Bi

S.W.

(2011). Preparing and application of polymerized aluminum-ferrum chloride. Adv. Mater. Res. 183–185, 1956.

, Zhang

, Zhou

, Wang

, An

, and Meng

(2014). Novel polyaluminum ferric chloride composite coagulant from Bayer red mud for wastewater treatment. Desalin. Water Treat., 52, 7645.

10.

H.W.

, Su

S.Q.

, Yang

, Cai

, Liu

, Yao

, and Peng

(2014). Preparation of potassium sulfate from K-feldspar by hydrothermal alkaline method:reaction principle and process evaluation. Ciesc. J., 8, 91.

11.

, Ma

H.W

, and Yang

(2016). Sintering preparation and release property of K2MgSi3O8 slow-release fertilizer using biotite acid-leaching residues as silicon source. Ind. Eng. Chem. Res., 55, 41.

12.

Mangrich

, Tessaro

, Anjos

A.D.

, Wypych

, and Soares

(2001). A slow-release K ⁺ fertilizer from residues of the Brazilian oil-shale industry: Synthesis of kalsilite-type structures. Environ. Geol., 40, 1030.

13.

Pérez

M.G.

, Rueda

J.I.P.

, Mateos

F.B.

, and Marín

J.P.

(1999). Slow-release fertilizer in the form of emulsion. Chem. Biochem. Eng. Q., 13, 21.

14.

Pino

J.S.N

.D., Padrón

I.J.A.

, Martin

M.M.G.

, and Hernández

J.E.G.

(1995). Phosphorus and potassium release from phillipsite-based slow-release fertilizers. J. Control. Release., 34, 25–29.

15.

Solihin , Zhang

, Tongamp

, and Saito

(2010). Mechanochemical route for synthesizing KMgPO₄ and NH₄MgPO₄ for application as slow-release fertilizers. Ind. Eng. Chem. Res., 49, 2213.

16.

Solihin , Zhang

, Tongamp

, and Saito

(2011). Mechanochemical synthesis of kaolin–KH₂PO₄ and kaolin–NH₄H₂PO₄ complexes for application as slow release fertilizer. Powder Technol. 212, 354.

17.

S.Q.

, Ma

H.W.

, Yang

, Zhang

, and Luo

(2014). Synthesis of kalsilite from microcline powder by an alkali-hydrothermal process. J. Miner. Metall. Mater., 21, 826.

18.

Tokunaga

(1991). Potassium silicate: A slow-release potassium fertilizer. Nutr. Cycling Agroecosyst., 30, 55.

19.

Tomaszewski

P.E.

, Mączka

, Majchrowski

, Waśkowska

, and Hanuza

(2005). Crystal structure and vibrational properties of KMg₄(PO₄)₃. Solid State Sci. 7, 1201.

20.

Wang

X.K.

, Zhang

Y.H.

, Lu

R.R.

, Zhou

F.S.

, An

, Meng

Z.L.

, Fei

, and Lv

F.Z.

(2014). Novel multiple coagulant from Bayer red mud for oily sewage treatment. Desalin. Water Treat., 54, 1.

21.

Wasilewski

, and Krukowski

(2004). Land conversion for suburban housing: A study of urbanization around Warsaw and Olsztyn, Poland. Environ. Manage., 34, 291.

22.

Xie

, Liu

, Ni

, Zhang

, and Wang

(2011). Slow-release nitrogen and boron fertilizer from a functional superabsorbent formulation based on wheat straw and attapulgite. Chem. Eng. J., 167, 342.

23.

Yao

, Hamada

, Sato

, Akiyama

, and Yoneyama

(2014). Identification of the major constituents of fused potassium silicate fertilizer. Trans. Iron Steel Inst. Jpn., 54, 990.

24.

Yuan

, Solihin , Zhang

, Kano

, and Saito

(2014). Mechanochemical formation of K–Si–Ca–O compound as a slow-release fertilizer. Powder Technol. 260, 22.

25.

Zhang

, and Solihin, Saito

(2009). Mechanochemical synthesis of slow-release fertilizers through incorporation of alumina composition into potassium/ammonium phosphates. J. Am. Ceram. Soc., 92, 307.

K 2 MgSi 3 O 8 in Slow-Release Mineral Fertilizer Prepared by Sintering of By-Product of Red Mud-Based Flocculant

Abstract

Abstract

Introduction

Experimental Details

Materials

Preparation of K2MgSi3O8 mineral fertilizer

Characterization

Solubility and release properties

Results and Discussion

Preparation of RMF

Solubility of RMF

Characterization of RMF

Release properties of RMF

Heavy metal dissolution

Cost analysis

Conclusion

Footnotes

Acknowledgments

Author Disclosure Statement

References

Preparation of K₂MgSi₃O₈ mineral fertilizer