Impact of HNO<sub>3</sub> Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield

Dick, Deborah P.; Costa, Janaina B. da; Leite, Anderson José B.; Brocchi, Eduardo A.

doi:10.21577/0103-5053.20160230

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Article • J. Braz. Chem. Soc. 28 (5) • May 2017 • https://doi.org/10.21577/0103-5053.20160230 copy

Impact of HNO₃ Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield

Authorship SCIMAGO INSTITUTIONS RANKINGS

In this study, changes on the chemical composition and on the humic acids yield of coal matrices promoted by 25% HNO₃ treatment were investigated, by means of elemental, thermogravimetric analyses, and Fourier transform infrared spectroscopy (FTIR). The "run of mine" (ROM) matrix C-MTR (ROM coal) showed the highest C content (41%), highest C/N ratio (76) and lowest ash content (54%) of the studied samples. In contrast, coal tailings presented a higher degree of aromaticity. Treatment with HNO₃ solution increased N content, but not that of C. Therefore, the C/N ratio of all samples decreased to values between 11 and 20. The insertion of N occurred in the aromatic structures, while the oxidation occurred in both the aromatic and aliphatic chains. HNO₃ treatment increased the humic substances content and the largest increase being observed in the coal tailings (16 to 31% increment in comparison to the untreated sample). The generated humic acids showed in general a chemical composition similar to that of soil humic acids, but a greater aromaticity degree.

Keywords:
humic substances; coal oxidation; FTIR spectroscopy; TGA

	C / %	N / %	H / %	C/N	H/C	Ash / %
C-MTR	41.20 ± 0.09^a a mean (n = 2) ± standard deviation; HF: samples demineralized with 10% HF solution.	0.55 ± 0.08	2.05 ± 0.37	75 ± 1.1	0.60 ± 0.11	54
R-MTR	16.21 ± 0.88	0.29 ± 0.01	1.52 ± 0.01	56 ± 0.3	1.12 ± 0.07	62
R-FOR	6.75 ± 0.34	0.16 ± 0.01	0.78 ± 0.04	42 ± 2.1	1.40 ± 0.07	78
RBC	11.74 ± 1.11	0.27 ± 0.06	1.00 ± 0.01	43 ± 0.6	1.02 ± 0.03	84
C-MTR_HF	64.48 ± 7.46	1.19 ± 0.20	3.72 ± 0.18	54 ± 2.8	0.69 ± 0.05	18
R-MTR_HF	62.12 ± 5.36	1.07 ± 0.08	3.73 ± 0.23	58 ± 0.4	0.72 ± 0.02	13
R-FOR_HF	25.80 ± 0.70	0.46 ± 0.03	1.34 ± 0.26	56 ± 0.7	0.62 ± 0.01	49
RBC_HF	15.10 ± 0.40	0.36 ± 0.20	9.30 ± 0.30	42 ± 2.8	0.74 ± 0.00	46

Sample	Relative intensity / %								Aromaticity index
Sample	RI₃₂₀₀	RI₂₉₂₀	RI₁₇₀₆	RI₁₆₀₈	RI₁₅₄₀	RI₁₄₃₀	RI₁₂₅₀	RI₁₀₃₀	I₁₆₃₀/I₂₉₂₀
C-MTR_HF	1.2	27.8	n.d.	34.6	n.d.	15.7	15.7	2.3	1.1
R-MTR_HF	2.5	13.7	n.d.	48.4	n.d.	9.4	21.3	3.4	2.0
R-FOR_HF	2.5	13.5	n.d.	49.0	n.d.	9.5	21.9	3.0	2.2
RBC_HF	2.1	18.6	n.d.	42.3	n.d.	17.7	13.7	3.3	2.0

Sample	Residue (T > 800 ºC) / %	Residue (T > 1000 ºC) / %	TGI I	TGI II
C-MTR_HF	71	62	3.43	4.85
R-MTR_HF	62	51	5.04	7.16
R-FOR_HF	65	56	3.05	4.32
RBC_HF	83	78	2.63	3.71
C-MTR_N-HF	49	49	1.77	2.27
R-MTR_N-HF	41	41	4.54	5.48
R-FOR_N-HF	59	36	1.23	2.59
RBC_N-HF	77	67	2.20	3.70

Sample	Yield^a a yield of treatment with 25% HNO3 solution;	C / %	H / %	N / %	C/N	H/C
C-MTR_N	91.95 ± 6.3^b b mean (n = 2) (standard deviation); N: HNO3 treated samples; N-HF: samples treated with HNO3 and demineralized with 10% HF.	37 ± 0.4	1.9 ± 0.5	2.6 ± 0.2	14 ± 0.0	0.61
R-MTR_N	67.26 ± 2.6	12 ± 1.2	1.1 ± 0.5	0.9 ± 0.1	13 ± 0.0	1.10
R-FOR_N	73.48 ± 0.3	8 ± 2.1	0.8 ± 0.6	0.7 ± 0.3	11 ± 0.0	1.20
RBC_N	91.66 ± 0.4	11 ± 1.7	0.5 ± 0.2	0.6 ± 1.1	20 ± 4.0	0.55
C-MTR_N-HF	-	65 ± 1.0	2.8 ± 0.9	4.6 ± 1.0	14 ± 0.0	0.52
R-MTR_N-HF	-	58 ± 1.0	2.2 ± 0.2	3.9 ± 1.4	16 ± 0.0	0.46
R-FOR_N-HF	-	55 ± 5.0	2.5 ± 0.8	4.0 ± 1.5	14 ± 0.0	0.55
RBC_N-HF	-	57 ± 8.0	2.6 ± 1.7	1.2 ± 1.0	47 ± 3.0	0.55

Sample	Relative intensity / %										Aromaticity index
Sample	RI₃₂₀₀	RI₃₀₃₀	RI₂₉₂₀	RI₁₇₀₆	RI₁₆₀₈	RI₁₅₄₀	RI₁₄₃₀	RI₁₃₃₀	RI₁₂₅₀	RI₁₀₃₀	I₁₆₃₀/I₂₉₂₀
C-MTR_N-HF	1.1	1.1	4.1	19.6	20.3	18.1	3.7	16.5	16.4	n.d.	4.9
R-MTR_N-HF	0.4	0.8	2.2	28.6	20.5	16.7	n.d.	14.3	16.5	n.d.	9.4
R-FOR_N-HF	n.d.	n.d.	5.7	23.1	17.7	17.1	2.3	16.2	12.5	5.4	3.1
RBC_N-HF	n.d.	n.d.	17.7	11.8	22.0	8.2	10.6	n.d.	16.5	11.4	1.2

Sample	C_HS / (g kg^-1)	C_FA / (g kg^-1)	C_HA / (g kg^-1)	C_HS/C_T	C_HA/C_HS
C-MTR^b b HNO3 untreated; N: HNO3 treated.	1.86 ± 0.05^a a Mean (n = 2) ± standard deviation;	1.76 ± 0.11	0.10	0.45	5.4
C-MTR_N	27.92 ± 0.99	0.67 ± 1.03	17.25	7.6	61.8
R-MTR^b b HNO3 untreated; N: HNO3 treated.	5.54 ± 0.70	2.70 ± 0.60	2.84	3.4	48.7
R-MTR_N	19.07 ± 0.96	3.64 ± 0.44	15.42	15.7	80.9
R-FOR^b b HNO3 untreated; N: HNO3 treated.	2.63 ± 0.41	2.40 ± 0.2	0.23	3.9	8.7
R-FOR_N	22.51 ± 0.61	3.69 ± 0.25	18.81	28.2	83.6
RBC^b b HNO3 untreated; N: HNO3 treated.	4.89 ± 1.71	3.18 ± 0.18	1.71	4.2	35.0
RBC_N	34.59 ± 1.25	14.18 ± 5.4	20.40	30.6	59.5

Sample	C / %	N / %	C/N
C-MTR_N	56.8	3.94	14
R-MTR_N	58.4	3.72	16
R-FOR_N	54.0	3.92	14
RBC_N	54.1	3.71	15

Sample	Relative intensity / %								Aromaticity index
Sample	RI₃₀₇₀	RI₂₉₂₉	RI₁₇₁₃	RI₁₆₁₀	RI₁₅₂₆	RI₁₃₃₈	RI₁₂₄₈	RI₁₀₈₀	I₁₆₃₀/I₂₉₂₀
HA C-MTR_N	0.7	2.1	29	21	18	13	13	n.d	10
HA R-MTR_N	0.8	1.6	32	24	16	10	14	n.d	15
HA R-FOR_N	0.8	3.1	33	20	15	11	11	3.9	6.5
HA RBC_N	0.7	2.8	30	20	16	12	11	5.0	9.3

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Impact of HNO3 Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield

Impact of HNO₃ Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield