FIELD OF THE INVENTION
The present invention relates to a process for the recovery of tin from tin sludge. More particularly, the
invention relates to physical, chemical and electrolytic method of recovery.
BACKGROUND OF THE INVENTION
Tin raw material is imported from other countries with high cost. Cost of tin is increasing day by day. During
the tin coating process, a considerable amount of tin is lost and is collected as sludge. Approximately 400
kg tin sludge is generated per month. Recovery of high purity metallic tin from sludge will be a cost saving
step for the tin coating plant.
Presently, available tin extraction technologies are costly. The tinning process is carried out by immersing
steel sheets in a molten tin bath or by electro plating process. Tin is coated as a thin coating, which protects
steel from aggressive corrosive medium and preserves food stuffs from poisoning by microbes.
Few organic and inorganic additives are also added to impart good adhesion on the steel surface. After the
tinning process, a small amount of sludge is left with Iron (Fe), Nickel (Ni), Copper (Cu) and Lead (Pb) as
minor constituents of oxides with tin oxide (90%) as the major one.
Few patents have been filed in the similar domain:
Patent No. KR101752727 relates to a method of recovering tin from tin waste. More specifically,
the invention relates to the method of recovering high-purity tin from tin waste, comprising: a step of
extracting crude tin using caustic soda; a step of electrolytic refining; and a step of vacuum refining.
Patent No. CN106092980 relates to the technical field of metallurgy analysis, and concretely
discloses a method for detecting tin in slag. The method comprises the following steps: 1, melting and
decomposing a sample to be detected with an alkali, and acidifying the molten and decomposed sample
with diluted hydrochloric acid; 2, adding a sodium hydroxide solution to a solution obtained in step 1 to
adjust the solution obtained in step 1 to be alkaline, adding sulfuric acid to adjust the pH value of the
alkaline solution to 0-1, and adding a thiourea and ascorbic acid mixed solution; and 3, converting tin in a
solution obtained in step 2 into a hydrogen stannide gas under the reduction action of potassium
borohydride, sending the hydrogen stannide gas to a quartz atomizer by using a carrier, carrying out
fluorescence determination, and obtaining the tin content according to the fluorescence intensity.
Patent No. CN105177623 proposes a method for recovering tin from a circuit board waste. The
method comprises the following steps: 1) pretreatment of the circuit board waste: a device on the circuit
board waste is dismounted; and a dismounted circuit board is reacted with diluted hydrochloric acid; 2) tin
dissolving: the circuit board reacted with the diluted hydrochloric acid in the step 1) is put in a leaching
tank containing SnCl4 solution for dissolving and filtering; and filtrate is tin-contained solution; and 3)

treatment of the tin-contained solution: the tin-contained solution obtained in the step 2) is extracted to a
diaphragm electrolytic bath for diaphragm electrodeposition to deposit simple-substance tin on a cathode,
wherein the diaphragm electrodeposition has the following parameter conditions: the current density is
300-800 A/m2, the temperature is 20-50 DEG C, and the electrode gap is 6-10 cm.
Patent No. CN104152701B provides a method for recycling tin from coarse tin refining slag. The
method comprises a leaching step, a purifying step and an electrodeposition step. According the leaching
step, the coarse tin refining slag and oxidizing agents are added into a hydrochloric acid system at the
temperature of 55 DEG C to 70 DEG C, and are leached for two to three hours, leaching liquid is obtained,
and the adding number of the oxidizing agents is 1.5 times to 2 times the required theoretical tin leaching
amount in the coarse tin refining slag; according to the purifying step, cleaning agents are added into the
leaching liquid, the leaching liquid is purified for 30 minutes to 120 minutes at the temperature of 20 DEG
C to 30 DEG C, purifying liquid is obtained, and the adding number of the cleaning agents is one time to
1.5 times the required theoretical foreign ion deposition amount; according to the electrodeposition step,
electrodeposition is carried out on the purifying liquid at the temperature of 30 DEG C to 40 DEG C, the
polar distance is four cm to five cm, the current density of electrodeposition is 170 to 250 A/m<2>,
electrodeposition is carried out for 10 to 15 hours, anolytes and crystal tin are obtained, the oxidizing
agents are the anolytes, and the tin in the coarse tin refining slag exists in a metal elementary substance
mode.
Copper and the tin contained in the coarse tin refining slag are thoroughly separated by adoption
of the oxidizing agents which are low in iron content and contain Sn4+, and therefore the purity and the
recycling rate of the obtained tin are improved. The method can efficiently recover tin from the circuit
board waste; and generated solution tin can be recycled.
Patent No. KR101486668 relates to a method of recovering tin in tin-containing waste, and more
specifically, to a method of recovering and separating equal to or greater than 98% of tin metal in tin-
containing waste by wet extraction which aims to increase recovery rate of expensive valuable metal by
easily recovering and treating high-purity tin in tin-containing waste. Provided is a method of recovering
and separating equal to or greater than 98% of tin metal in tin-containing waste by wet extraction which
includes a first step of injecting tin-containing waste (solute) and nonoxidative inorganic acid (solvent),
selected from sulfuric acid having equal to or less than 50% concentration and hydrochloric acid having
equal to or less than 50% concentration, in a weight ratio of 1:1-1:2.0 in a reactor to be mixed to form
tartrate solution (S1); a second step of injecting zinc powder into the tartrate solution to extract tin content
in accordance with ionization tendency (S2); a third step of filtering the tin content extracted as above
(S3); and a fourth step of injecting the tin content into a heating furnace with flux to be heated in 300-
400°C in order to form a molten tin solution (S4).
Patent No. CN103436885 provides a method suitable for recycling waste liquor in a tin removing
procedure of a circuit board industry, and the method is suitable for the recycling of tin removal waste

liquor which takes nitric acid as a main component and contains heavy metal compounds, such as namely
tin, copper, and the like. The method comprises the following steps of: treating heavy metals contained in
the tin removal waste liquor by adopting a complexing precipitation method, and depositing metal ions
contained in the tin removal waste liquor. According to the invention, after the tin removal waste liquor is
subjected to solid-liquid separation, metal resources, such as namely the tin, the copper, and the like, can
be recovered from deposits; clear liquor and new tin removal liquor are similar in component and are
recycled in the tin removing procedure after being appropriately regulated, so that the purpose of recycling
of the tin removal waste liquor is realized. The method provided by the invention can realize the recycling
of the tin removal waste liquor, can be used for efficiently recovering the metal resources contained in the
waste liquor, has the advantages of simple process, small equipment investment, low energy consumption
and no waste water and waste gas discharge in an operating process and realizes the clean production of
the tin removing procedure.
According to the publication by Amit Chaurasia et al (Amit Chaurasia*, K. K. Singh, T. R. Mankhand,
International Journal of Metallurgical Engineering 2013, 2(2): 243-248 DOI: 10.5923/j.ijmee.20130202.17),
printed circuit board (PCB) waste is generally dumped as a land filling or treated pyrometallurgically, which
generates hazardous gases and also destroys valuable PCB components. For recycling of the components,
dissolution of solder in hydrochloric and nitric acids of different concentrations was studied. Nitric acid was
found to be suitable for the extraction of copper and tin at room temperature.
Jian-Guang Yang et al (Yong-Tan Wu and Xu-Liang Zhan, Mineral Processing and Extractive
Metallurgy (Trans. Inst. Min. Metall. C) 2014 VOL 123 NO 4. DOI:10.1179/1743285514Y.0000000070)
reports the separation of tin from a low-grade tin concentrate through leaching and low-temperature
smelting processes. Parameters such as hydrochloric acid concentration, leaching temperature, smelting
temperature, flux composition and tin yield were reported. Maximum recovery of 97.66% with 97.48%
purity of tin was extracted at 870°C smelting temperature.
Zoltánharangi–tamáskékesi (Materials Science and Engineering, Volume 39, No. 2 (2014), pp. 13–
22) discloses that soldering scrap from the electronic industry produces oxide dross, composed mainly of
SnO2. By converting SnO2 into a soluble form by carbothermic reduction using coke powder between 800–
1000o C, the treated dross and the products were separated by leaching with boiling 6 mol dm –3 HCl
solution and the conversion rates were higher than 90% of the originally insoluble tin-dioxide content.
Nonot Soewarno et al (Nonot Soewarno, Ali Altway, Susianto, Fadlilatul Taufany, Siti Nurkhamidah,
IPTEK, Journal of Engineering, Vol. 1, No. 1, 2014) reports that slag is a mixture of mineral in tin sand or
by product in the smelting process. Tin can be separated from other minerals in by solvent extraction to
obtain a stannate chloride by using hydrochloric acid (HCl). The recovery of tin increases with the extraction
temperature and solvent concentration. The highest recovery of 61.5% is obtained at 80 ºC, concentration
of HCl is 10 wt.%, with a HCl solution and slag ratio is 7: 1.

Hao Cui and Corby G Anderson ( J Adv Chem Eng 2016, 6:1 Volume 6 • Issue 1 • 1000142, DOI:
10.4172/2090-4568.1000142) disclose the processing of waste printed circuit boards by physical,
pyrometallurgical and hydrometallurgical processes for the recovery of precious metals from them. This
review emphasizes the recycling of PCBs by physical and hydrometallurgical treatments.
Syarifah Aminah Ismail et al (Syarifah Aminah Ismail, Noorina Hidayu Jamil, H.Kamarudin and
Mohd Arif Anuar Mohd Salleh, Applied Mechanics and Materials Submitted: 2015-01-06 ISSN: 1662-7482,
Vols. 754-755, pp 571-575 Accepted: 2015-01-06, doi:10.4028/www.scientific.net/AMM.754-755.571)
disclose a process whereby solder dross containing Sn, Ni, Cu, Zn, Fe and other impurities was leached
with 0.1-1.0M citric acid at 60 °C for 24 hours stirring times. Parameters affecting the tin recovery such as
acid concentration, stirring time and temperature were investigated. Results had shown that the recovery
of tin from solder dross was 99.0%.
Sungkyu Lee et al (Sungkyu Lee, Kyoung-Hoon Kang, Jae Layng Park, Myung-hwan Hong, Soo-
Young Lee, Sung-Su Cho and Hyun Seon Hong, Current Nanoscience, 2014, 10, 104-107) report that waste
PCBs from LCDs contain valuable metals like Sn, Cu, and other noble metals. High purity tin was obtained
by electro-winning, by HCl leaching after preliminary HNO3 dissolution step. Direct one-step leaching in
H2SiF6 + H2SO4 + H2O2 followed by electro-winning was done for mass production. Tin with 96% purity
and 93.2% recovery was obtained.
Manis Kumar Jha et al (Manis Kumar Jha, Pankaj Kumar Choubey, Amrita Kumari Jha, Archana
Kumari, Jae-chun Lee, Vinay Kumar a, JinkiJeong, Waste Management 32 (2012) 1919–1925) report that
printed circuit boards (PCBs) are the most valuable resources for recovery of tin from waste (PCBs),
containing 52.6% Sn and 47.3% Pb. The experimental data indicate that 95.79% of tin was leached out
from solder using 5.5 M HCl at 90 °C in mixing time. About 97.79% of tin was leached out from solder
materials. From the leach liquor, the precipitate of sodium stannate was obtained at pH 1.9. The Pb from
the leach residue was removed by using 0.1 M nitric acid at 90 °C in mixing time 45 min and pulp density
10 g/L. The metal free epoxy resin could be disposed-of safely/used as filling material without affecting the
environment.
M. Ranitović et al (M. Ranitović, ž. Kamberović, m. Korać, n. Jovanović, a. Mihjalović, METALURGIJA
55 (2016) 2, 153-156) disclose the selective recovery of Pb and Sn from WPCBs using NaOH, HCl and
HNO3,. About 98 % of Pb can be leached using 2 M HNO3 solution at 80 °C and over 90 % of Sn using 2 M
HCl solution at 80 °C, independently.
Tamas Kekesi (Acta Metallurgica Slovaca, Vol. 19, 2013, No. 3, p. 196-205) relates to the recycling
of impure tin by electrorefining process. The hydrochloric acid tin chloride electrolyte can be applied by
optimizing the solution composition and the current parameters. Strong chloro – complex formation in the
hydrochloric acid solution enhance stability of the Sn (II) species and promotes a cathodic deposition of
acceptable quality. The current efficiency and the morphology were improved by applying periodically

reversed (PCR) current. Dendritic crystal growth was seen. The cathode deposit is easily removed, melted,
and the recycled tin of high purity.
L. A. Castro and A. H. Martins (Brazilian Journal of Chemical Engineering Vol. 26, No. 04, pp. 649
- 657, October - December, 2009) disclose the extraction and recovering of tin and copper by leaching
followed by precipitation from the scraps from printed circuit boards. The milled powder was leached by
using 2.18N H2SO4, 2.18N H2SO4 + 3.0N HCl, 3.0N HCl, and 3.0N HCl + 1.0N HNO3. About 98% for Sn and
93% for Cu have been extracted in 3.0N HCl + 1.0N HNO3 leaching solution.
Jae Woo Ahn and Jae Chun Lee (Materials Transactions, Vol. 52, No. 12 (2011) pp. 2228 to 2232)
relate to the recovery of tin (Sn) from the scraps or plating sludges by a hydrometallurgical process with
metals such as, As, Sb, Bi, Cu, Zn and Pb. A solvent extraction process using TBP (tri-n-Butylphosphate)
as the extracting reagent at various concentrations of hydrochloric acid and sodium chloride was studied.
The study showed that Pb, Bi, Cu, Zn and Sb were quantitatively removed by scrubbing with 8.0 mol/L HCl
from the organic phase. The purity of finial Sn strip solution was 98.9% and the recovery of Sn was 67.9%.
F.A. López et al (F.A. López, I. Martín, F. J. Alguacil, O. Rodríguez, I. García-Díaz, E. Escudero)
investigate the recovery and purification of tin from tin solder slag by an electrorefining process in a tin
(II)- sulphuric acid medium as electrolyte. Different variables such as current density and electrolyte flow
were studied. The purity of the deposited tin increases from 64.4 % to 99.93 %, with the recovery of
valuable metals which concentrated in the anodic slimes.
However, the need exists in the art to provide a process for the recovery of tin from tin sludge by
cost-effective method and environment- friendly.

Objects
An object of the invention is to provide a process for recovering tin from tin sludge that is environment
friendly.
An object of the invention is to provide a process for recovering tin from tin sludge that is cost effective.
Disclosure of the Invention
A process for recovering tin from a tin sludge is described comprising steps of drying the tin sludge, grinding
the tin sludge into a fine powder, washing the fine powder with a solvent to remove organic compounds in
the tin sludge followed by filtration, forming a filtrate and a cake, fusing the cake at 850 - 900°C with an
alkali, forming alkali stannate (Na2SnO3) and Meta stannic acid (SnO(OH)2, treating the alkali stannate
(Na2SnO3) and Meta stannic acid (SnO(OH)2 with HCl to form an electrolyte, where the Sn4+ is in the form
of hydroxides and complex stannic chloride; and performing electrolysis over the electrolyte to deposit tin
over cathode.
Brief Description of Drawings
FIG. 1 shows a process with various steps for recovering tin from a tin sludge.
FIG. 2 is a scanned electron microscopic image of tin sludge in an experimental analysis.
FIG. 3 is a scanned electron microscopic image of Na2SnO3 in an experimental analysis.
Description of Preferred Embodiment
In accordance with an embodiment of the invention various steps of a process (100) has been
shown in FIG. 1 for recovering tin from a tin sludge.
The tin sludge in an embodiment can be a plant waste.
At step 104, the tin sludge is being dried. The tin sludge is dried in hot air oven at 150 °C and
ground into a very fine powder step 108.
Trace level of impurity oxide namely FeO, PbO, CuO are generally present in the tin sludge, which
are identified by XRF and XRD analysis. These oxides interfere in the deposition of tin on the cathode during
electrolysis that needs to be avoided.
They are removed by selective precipitation process. They are coagulated and settled and
separated to selective filtration through filtering media, 41 filter papers / whatman filter. This process is

done after the formation of sodium tin oxide by treating with sodium hydroxide and subsequent dissolution
process in hot water (will be discussed in the later steps).
At step 112, the finely ground powder is washed with a solvent and the organic compounds are
removed by trapping into the solvent and filtered. Under the optimized conditions the organic solvents
trapped the unwanted organic compounds by dissolution forming a solution containing methane sulphonic
acid, Hydroquinone (benzene 1,4 Diol).
The composition of the tin sludge post solvent treatment (step 112) is being shown in Table 1

The solvent in the embodiment of the invention is an ethanol or acetone or benzene.
After being washed at step 112, solvent is extracted and the left is a cake. The cake is comprised
of tin oxide associated with small amount of other metal oxides like CuO, NiO. Fe2O3.
At step 116 the cake obtained is fused with an alkali. The alkali in an embodiment is NaOH. The
tin oxide present in the cake reacts to sodium hydroxide forming alkali stannate (Na2SnO3) and Meta stannic
acid (SnO(OH)2. The temperature maintained while fusion is 850 - 900°C.
SnO2 (s)+2NaOH (l) = Na2SnO3 (l) + H2O (g)
With the higher pH of the electrolyte solution there is a possibility of precipitation of tin hydroxide
and oxy hydroxide, which may lead to the inhibition of electro deposition of Sn4+ to Sn metal during the
cathodic deposition process. Hence the electrolyte is slightly acidified by the addition of dil HCl to bring
down the pH of the solution less than 10 (step 120). Precisely the pH of the electrolyte is maintained
between 8-10. This leads to the formation of Sn4+ in the form of hydroxides and complex stannic chloride.
The treated solution containing tin ions formulated in electrolyte for the deposition of tin at the cathode.
The acid used is 0.25-1.0 M HCl.
At step 124, electrolysis is performed on said electrolyte, to deposit tin over cathode. An
electrolytic cell is designed with suitable anode and cathode made up of lead / lead alloy and steel plates
respectively with an electrical distribution system connected to a power source.

Lead and lead alloy are most stable and disintegrate in alkali solution. So, the Pb alloy is being
used as the anode in electrolytic cell.
In most of the electro deposition process stainless steel is being used as the cathode. Because it
has some very fine and mirror polished surface which leads to adhere the tin metal during electrolysis
and at the end of the process the tin metal can be peeled off smoothly from the SS surface.
In another embodiment, the anode is graphite.
On electrolysis, tin is deposited as fine coating on a cathode surface where the morphology can be
changed from uniform to dendritic deposit depending upon the current and voltage characteristics in the
electrolytic cell. After the termination of electrolysis, the cathode product is removed and washed with
distilled water. A sheet of tin is obtained as the product at low current density and a powdery deposit is at
high current density.
The product purity is assessed by XRD, XRF and AAS techniques and found that the purity is ranging
between 90 - 99%.
The cathode current density varies between 20 A/dm2 - 25 A/dm2. The cell voltage is maintained
at 2.0 to 15V and the temp of 70 - 80°C.
In any chemical reaction, the temperature influences the reaction rate, which also similar in
electrochemical reaction. Till the reaction proceed at diff temp from 70-80 C in order to identify the quantity
of metal deposition with respect to temp, which ascertain from the experiments about 70°C is found to be
optimum, which will helps in smooth and coherent deposit of tin at the SS cathode, which can be easily
peeled off from the cathode.
Experimental Analysis:
Following steps were performed:
The tin sludge was dried then grounded into a very fine powder.
The tin sludge was washed with ethanol to remove organic compounds forming a filtrate and a cake.
The cake was fused at 850 - 900°C with NaOH, forming alkali stannate (Na2SnO3) and Meta stannic acid
(SnO(OH)2.
The alkali stannate (Na2SnO3) and Meta stannic acid (SnO(OH)2 was treated with HCl (1M) to form
an electrolyte, where the Sn4+ in the form of hydroxides and complex stannic chloride.
Electrolysis was performed over the electrolyte to deposit tin over cathode.
Following were the parameters of electrolysis:

Anode: lead alloy
Cathode: stainless steel
Cell voltage is 2.0-15 V.
Cathode current density: 20 A/dm2 - 25 A/dm2
pH of the electrolyte: 8-10
The electrolysis was performed between 70 - 80°C for a predetermined period. After the completion
of electrolytic process, the cathode was removed and washed with distilled water. A uniform deposit of tin
either as thin sheet or in a powdery form was obtained depending upon the bath composition and current
density. The product was examined for its purity by using XRD, XRF and AAS analyses.
Scanned electron microscopic image of Sn sludge and Na2SnO3. is shown in FIG. 2 and FIG. 3.
The process mentioned above for recovering tin from tin sludge that is environment friendly and is
cost effective.

We Claim:
1. A process for recovering tin from a tin sludge, the process comprising:
drying the tin sludge;
grinding the tin sludge into a fine powder;
washing the fine powder with a solvent to remove organic compounds in the tin sludge followed
by filtration, forming a filtrate and a cake;
fusing the cake at 850 - 900°C with an alkali, forming alkali stannate (Na2SnO3) and Meta stannic
acid (SnO(OH)2;
treating the alkali stannate (Na2SnO3) and Meta stannic acid (SnO(OH)2 with HCl to form an
electrolyte, where the Sn4+ is in the form of hydroxides and complex stannic chloride; and
performing electrolysis over the electrolyte to deposit tin over cathode.
2. The process as claimed in claim 1, wherein composition of sludge post treatment with the
solvent is

3. The process as claimed in claim 1, wherein HCl is 0.25-1.0 M.
4. The process as claimed in claim 1, wherein anode for electrolysis is made up of lead or lead
alloy or graphite.
5. The process as claimed in claim 1, wherein cathode for electrolysis is made up of stainless
steel.
6. The process as claimed in claim 1, wherein cell voltage is 2.0-15 V.
7. The process as claimed in claim 1, wherein cathode current density during electrolysis is 20
A/dm2 - 25 A/dm2.
8. The process as claimed in claim 1, wherein the alkali is NaOH.
9. The process as claimed in claim 1, wherein the solvent is ethanol or acetone or benzene.
10. The process as claimed in claim 1, wherein pH of the electrolyte is 8-10.
11. The process as claimed in claim 1, wherein temperature of the electrolyte is 70-80 Deg. C.