Potential of phosphorus recovery from sludge-based hydrochar by wet chemical method

doi:10.11949/0438-1157.20210835

Abstract

Abstract:

Taking the phosphorus-rich sludge hydrothermal charcoal as the research object, the SMT method is used to analyze the phosphorus form distribution, and hydrochloric acid and citric acid are used as extractants to explore the potential of wet chemical recovery of phosphorus. The experimental results show that after hydrothermal carbonization of sludge, the total phosphorus content increased, the organic phosphorus is transformed into inorganic phosphorus, and the non-apatite inorganic phosphorus is transformed into apatite inorganic phosphorus. The forms of phosphorus in hydrochar are mainly inorganic and non-apatite inorganic phosphorus. Acid concentration, liquid-solid ratio and acid leaching time have significant effects on phosphorus leaching from hydrochar. Under the suitable acid leaching conditions (hydrochloric acid concentration 0.3 mol/L, liquid-solid ratio 50 ml/g, acid leaching time 240 min; citric acid concentration 0.1 mol/L, liquid-solid ratio 50 ml/g, acid leaching time 600 min), the phosphorus leaching efficiency of hydrochloric acid and citric acid can reach 94.34% and 88.78%, respectively. The pseudo-second order kinetic model can fit the leaching process of phosphorus in the two acid leaching systems well. Meanwhile, the leaching capacity of metal elements increased gradually with the increase of acid leaching time, and there is a linear correlation with the leaching capacity of phosphorus. The order of leaching capacity from large to small metals is Fe > Ca > Al >Mg. In addition, some heavy metal elements are also leached, and the order of leaching ability is Zn > Mn > Cr > Cu > Pb. After acid leaching, hydrochar has more pore structure, which is expected to be a good adsorption material.

Key words: sludge, hydrochar, phosphorus recovery, hydrochloric acid, citric acid, acid leaching

摘要：

以富含磷的污泥水热炭为研究对象，用SMT法分析磷的形态分布，以盐酸和柠檬酸为浸提剂，探究湿化学法回收磷的潜能。结果表明，污泥经水热碳化后，总磷含量上升，有机磷朝着无机磷转化，非磷灰石无机磷朝着磷灰石无机磷转化，水热炭中磷形态以无机磷和非磷灰石磷为主。适宜酸浸条件下（盐酸浓度0.3 mol/L、液固比50 ml/g、酸浸时间240 min，柠檬酸浓度0.1 mol/L、液固比50 ml/g、酸浸时间600 min），盐酸和柠檬酸对磷的浸出效率分别可达94.34%、88.78%，准二级动力学模型能较好地拟合磷的浸出过程；同时，金属浸出能力随酸浸时间延长而逐渐上升，与磷浸出能力呈线性相关，由大到小依次为Fe>Ca>Al>Mg；重金属浸出能力由大到小依次为Zn>Mn>Cr>Cu>Pb；酸浸残渣有望成为性能良好的吸附材料。

关键词: 污泥, 水热炭, 磷回收, 盐酸, 柠檬酸, 酸浸

CLC Number:

X 705

Jin XU, Jiedong ZHU, Juanli LI, Mengqiu LIU, Heluo GONG. Potential of phosphorus recovery from sludge-based hydrochar by wet chemical method[J]. CIESC Journal, 2021, 72(11): 5779-5789.

许劲, 朱杰东, 李卷利, 刘孟秋, 龚河洛. 湿化学法回收污泥水热炭中磷的潜能研究[J]. 化工学报, 2021, 72(11): 5779-5789.

Figures/Tables 17

Table 1 Basic physicochemical properties of sludge and hydrochar

样品	工业分析^①/%（质量）			元素分析^①/%（质量）					H/C	O/C	炭产率/%
样品	Ash	VM	FC	C	H	N	S	O	H/C	O/C	炭产率/%
污泥	56.48	40.57	2.95	20.16	3.5	2.9	0.9	16.07	2.08	0.6	—
水热炭	72.86	24.32	2.82	14.59	2.31	1.47	0.53	8.24	1.9	0.42	74.67

Table 2 Contents of metals and heavy metals in sludge and hydrochar

样品	金属含量/(mg/g)^①				重金属含量/(mg/kg)^①
样品	Fe	Al	Ca	Mg	Pb	Cu	Cr	Mn	Zn
污泥	92.15	41.84	18.99	10.58	29.04	73.12	50.11	552.53	474.62
水热炭	98.97	47.53	20.35	11.23	37.66	94.54	61.54	669.73	589.24

Fig.1 The fractional extraction process of phosphorus form based on SMT method

Table 3 Single factor experimental design

盐酸

柠檬酸

水热炭质量：0.4 g

液固比：50 ml/g

酸浸时间：720 min

酸浓度

0.01、0.05、0.1、0.15、0.3、0.5、0.8、1 mol/L

酸体积：20 ml

盐酸浓度：0.3 mol/L

柠檬酸浓度：0.1 mol/L

酸浸时间：720 min

液固比

10、15、25、50、100 ml/g

液固比：50 ml/g

盐酸浓度：0.3 mol/L

柠檬酸浓度：0.1 mol/L

酸浸时间

15、30、45、60、90、120、180、240、360、480、600、720 min

Table 4 Contents of different forms of phosphorus in sludge and hydrochar

样品	含量/(mg/g)
样品	TP	IP	NAIP	AP	总磷回收率R/%
污泥	22.89±0.18	20.70±0.38	15.77±0.27	5.59±0.21	—
水热炭	30.31±0.28	28.29±0.17	20.39±0.10	7.85±0.01	98.81

Fig.2 Percentages of phosphorus of different forms in total phosphorus in sludge and hydrochar

Fig.3 XRD patterns of sludge and hydrochar

Fig.4 Influence of different acid concentrations on phosphorus leaching efficiency

Fig.5 Influence of different liquid-solid ratios on phosphorus leaching efficiency and pH value of leaching solution

Fig.6 Influence of different acid leaching time on phosphorus leaching efficiency

Fig.7 Influence of acid leaching time on phosphorus leaching capacity in hydrochar

Table 5 Fit parameters of phosphorus release kinetics model in hydrochar

数学模型	酸浸体系	表达式	相关参数值	R²
Elovich模型	柠檬酸	$q = 0.2349 l n t - 0.6033$	α=0.3264; β=4.2571	0.9856
Elovich模型	盐酸	$q = 0.0994 l n t + 0.3665$	α=401.71; β=10.06	0.7775
准二级动力学模型	柠檬酸	$t q = 0.0304 t + 4.6582$	q_e=32.89; k₂=1.9839×10^-4	0.9861
准二级动力学模型	盐酸	$t q = 0.0351 t + 0.3477$	q_e=28.49; k₂=2.6448×10^-4	0.9999

Table 5 Fit parameters of phosphorus release kinetics model in hydrochar

数学模型	酸浸体系	表达式	相关参数值	R²
Elovich模型	柠檬酸	$q = 0.2349 l n t - 0.6033$	α=0.3264; β=4.2571	0.9856
Elovich模型	盐酸	$q = 0.0994 l n t + 0.3665$	α=401.71; β=10.06	0.7775
准二级动力学模型	柠檬酸	$t q = 0.0304 t + 4.6582$	q_e=32.89; k₂=1.9839×10^-4	0.9861
准二级动力学模型	盐酸	$t q = 0.0351 t + 0.3477$	q_e=28.49; k₂=2.6448×10^-4	0.9999

Fig.8 Influence of acid leaching time on the leaching capacity of phosphorus and metal elements(a) lemon acid leaching system; (b) hydrochloric acid leaching system

Fig.9 Relationship between leaching capacity of metal elements and phosphorus elements(a) lemon acid leaching system; (b) hydrochloric acid leaching system

Table 6 Leaching concentration of heavy metals under optimum acid leaching conditions

酸浸体系	浸出浓度/(mg/L)
酸浸体系	Pb	Cu	Cr	Mn	Zn
柠檬酸	0.04	0.05	3.36	6.36	8.66
盐酸	0.41	1.46	3.60	6.43	12.02

Fig.10 Leaching capacity of heavy metals under optimal acid leaching conditions

Fig.11 SEM-EDS analysis results of hydrothermal carbon (a), acid leaching residue of hydrochloric acid (b) and acid leaching residue of citric acid (c) respectively

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