Recovery of copper from small grain size fractions of municipal solid waste incineration bottom ash by means of density separation

Figures & data

Figure 1. Scheme of the rotating system of the centrifugal concentrator with implied mass and water streams: (1) feed funnel, (2) concentrator bowl, (3) counterflow water chamber and (4) rotating steel chamber connected to the impeller.

Figure 2. Scheme of the test rig: (1) water tap, (2) nozzle for spreading of tap water, (3) funnel and vibrating chute for proportioning the aggregates, (4) funnel for suspending and feeding of the concentrator bowl, (5) centrifugal concentrator, (6) water tank with wet-pit pump, (7) manometer and (8) settling chamber.

Figure 3. Batch 1 of material B before (left) and after (right) impact by the high speed rotation accelerator; images taken by an optical digital microscope.

Figure 4. Particle size distributions (density distribution: red-axis; cumulative distribution: black-axis) of material B.

Figure 5. Material C; image taken by an optical digital microscope.

Figure 6. Particle size distributions (density distribution: red-axis; cumulative distribution: grey-axis) of material C.

Figure 7. Enrichment factors for material C related to the mass yield (logarithmic scale); each point of the curves refers to a specific rotational speed level (from high to low mass yields: 437, 510, 583, 655 and 729 rpm).

Table 1. Coding for the investigations based on the design of experiments (DOE).

Run	Coding of the factor levels		Response
	Factor 1	Factor 2
1	−1	−1	Z 1
2	−1	0	Z 2
3	−1	1	Z 3
4	0	−1	Z 4
5	0	0	Z 5
6	0	1	Z 6
7	1	−1	Z 7
8	1	0	Z 8
9	1	1	Z 9

Table 2. Copper contents in the sieve fractions of the material B before and after impact.

Sieve fraction	Batch 1	Batch 1	Batch 2	Batch 2
	Before	After	Before	After
μm	g/kg	g/kg	g/kg	g/kg
0–63	5.05	4.84	1.67	1.73
63–125	4.98	4.90	1.46	1.50
125–200	5.27	4.63	2.16	1.80
200–630	8.14	4.87	1.69	1.59
630–2000	8.84	4.85	3.37	0.94
2000–4000	4.07	2.20	0.67	5.96

Table 3. Copper and lead contents in the sieve fractions of the material C.

Sieve fraction	Copper	Lead
μm	g/kg	g/kg
0–45	4.37	1.53
45–63	6.97	1.64
63–90	3.78	1.38
90–125	6.44	1.49
125–180	6.37	1.33
180–250	9.22	1.27
250–355	8.76	1.76
355–500	3.13	1.91
500–710	3.79	3.38

Table 4. Mass yields (R _M ), and contents, enrichment factors (i) and valuable yields (R _V ) for copper in the sieve fractions <250 μm of the Alpha line.

Sample		Copper content			Copper enrichment
	R M	Feed	Concentrate	Tailing	i	R V
	(%)	(mg/kg)	(mg/kg)	(mg/kg)	(–)	(%)
Batch 1 – before	1.43	4413	38430	3858	8.7	12.4
Batch 1 – before	1.76	4413	27022	4029	6.1	10.8
Batch 1 – after	1.69	4980	44004	3952	8.8	14.9
Batch 1 – after	1.91	4980	43995	3824	8.8	16.9
Batch 2 – before	1.58	2194	20694	1418	9.4	14.9
Batch 2 – before	1.36	2194	24644	1539	11.2	15.3
Batch 2 – after	1.36	2045	19975	1622	9.8	13.3
Batch 2 –after	1.96	2045	13498	1757	6.6	12.9

Figure 8. Valuable yields for material C related to the mass yield (logarithmic scale); each point of the curves refers to a specific rotational speed level (from high to low mass yields: 437, 510, 583, 655 and 729 rpm).

Figure 9. Lead contents in the concentrates of the investigations with material C in relation to the copper contents (black circles – data from investigations displayed in Figure 7 and 8, red diamonds – data from investigations listed in Table 5).

Table 5. Results of the DOE runs with material C: factor levels of the rotational speed and the counterflow pressure; mass yields and density of the concentrate, enrichment factors and valuable yields for copper.

Input Factors		Concentrate		Copper
Counterflow pressure	Rotational speed	Mass yield	Density	Enrichment factor	Valuable yield
(bar)	(rpm)	(%)	(g/cm^3)	(–)	(%)
2.25	481	0.67	4.03	37.6	25.3
2.25	510	1.04	3.57	32.6	34.1
2.25	539	1.15	3.50	23.2	26.6
2.50	481	0.42	4.43	49.0	20.7
2.50	510	0.88	3.66	29.3	25.8
2.50	539	1.06	3.52	29.0	30.8
2.75	481	0.48	4.25	50.3	24.4
2.75	510	0.60	3.99	49.3	29.5
2.75	539	0.60	3.74	43.1	26.0

Table 6. Results of the DOE assessment with material C: calculated linear and quadratic effects related to the mass yields (R _M ) as well as to the enrichment factors (i) and valuable yields (R _V ) for copper and for lead, respectively.

	Concentrate	Copper		Lead
	R M	i	R V	i	R V
	(%)	(–)	(%)	(–)	(%)
Linear effect counterflow pressure	−0.39	16.5	−2.0	22.3	2.5
Linear effect rotational speed	0.41	−13.9	4.4	−28.0	−4.7
Quadratic effect counterflow pressure	−0.06	7.2	3.7	3.7	4.8
Quadratic effect rotational speed	−0.22	3.2	−8.3	6.4	−6.9