Az~ract - Recocery of rhodium and m&e! ions !‘rom piarmg vliaste water lvas investigated. !r kv~as ‘ounc kat a hydrogen form cation-exchange resin can be used for the removal of the noble metal ions and that ,hese ions, especially rhodium. can easily be &ted from the resin with 1 N sulflrric acid; the elated solution can bs: recycled to the rhodium plating bath.

.Metal plating, especially of noble metals, is widely _~ed in Sapan. Noble metal ions, SAC; as rhodium and nic!~el, are not usually recycled but are lost in waste water in c~~ce~t~at~~~$ of 30 - 100 ppm. The recovery and recia.im of such metal ions was considered useful from :he itandpoin?t of resource conservation and of re+hlizing waste water. The authors have Investigated a number of ion-exchange phenomena[i -. S]. Thus s the feasibility of emplo$ng 3ich an ~~~-exc~~~~ge method fb;r the treatment of rho ium and nickel ions was examined ir, detalb.

itsubishi Kasei, Japan), a macroreticuzr sulfomc acid cation; exchange ~sln., was The resin particles were pre-treated in a column ilh ~yd~~c~~o~~c HGid (1 M) and

sodium hydroxide (1 M) aqueous solutions, and then wit ethanol and water. After this rGn was converted to the hydrogen form with excess 1 M ~~d~~c~~~~~c acid.

gs with water and alcohol wer carried Out before drying at 80°C for 3 hr. Y:7e

‘n a desiccator with a r.h. of 1 070. All chemicals were analyticai reagent grade cxmmercial materials and were used without further ~~~rif~cati~~.

The c~~ce~t~at~Q~ of rhodium and nickei ions wp/is determined by the use of a 205 exmic absorptkm spectrometer (Hitachi aku, Japan). ‘-‘isible spectra of nickel ions in various a cautions were obtained with a h 5000 $~ect~~~~~t~rnet~~ (Shimazu Seisaku, Japan). T

___ Manuscript received 77 June, 1980. Revised manuscript receivei. 24 March, :98:..

239

En order to study the removal ?~ehavior of nickel an rhodium ions on t e hydrcagem fom cation exchange resin (R - H+)y 1 g of the resin f weighed into the glass column (length, 300 n-ml, diam, BO m-n), and resin was con ned as necessar)r witi? ~yd~~c~~Q~~~ or sulfuric acid aqueous solntisns wat lo- 5 - 6 N. According to the column condition, 50 ml af 100 ppm nickel or rhodlium a~~e~~s solutions ranging jn acid conce~t~ati~~ frmn 1W5 to 6 N ere passed at. a flow rate of I mUmin, f~~~~~~~ by 50 ml of pure water. Each of the passe solutions (100 rnB> were analyzed by atomic absorption spectrometry. con ation of 100 ppm was selected as typical of the concentration of waste wat ntai nickeli or r~~d~~~ ions.

ova’s the removai ratios of nickel ions during co1 eratisn. As can b

nickel ions are removed by acid solutions in con owever, the ratios of t emoved nickel ion t63 the origin

concentrations increased from S to by the 6 I‘d acid solution (remova ions in sulfuric acid so~~t~o~5 of strengt

Fig. 1. Removal of nickel ions ia various acid solutions on a hydrogen form cation-exchange resin.

Table 1. Remova! of rhodium ions in various sulfuric acid solutions on hydrogen form cation-exchange resin

Acid concentration (N) 1w 1%3 IQ-1 1 3 6

Removal ratio (To) 96 93 68 35 10 I.5

Figure 2 presents the visible spectra of the n.ickd ions in IO-’ and 6 soiutions. As shown in this figure, the behavior is aknost the same in bo exception of a slight difference in the absorption peaks mar 400 mm wave leng XX&, it is ~~~~~,~~e~ that the difference In the dissdved states of nickei ions w :he different acid concentrations and thus, almost all the

except for a slight resence of [Ni(H, e 6 N acid solutrsn. ematically represents the ~~~§~~~~$~t of beat of the exchange reaction. 1-t was

iO-‘N

G!oss ampode

Reference srdie Sample sde

Fig. 3. Sshernat,c diagram of the measurement oi” heat of the excirange reaction between hydtogerr onb BAA rhOChIT iObiS.

242 TAKXSIiI SUZUKl et ai.

found that fhe reaction was slightly endothermic and that the va’iue of the heat of reaction was small (0.25 kJ/equivalent of R-H*). From this result it was inferred that rhodium ions existed in both the trivalent and univalent states, i.e. h3+ aud [Wh(SO,)]+ ou the fohowing basis of Suzuki’s classification of the heats of i~~-~x~~a~ge reactions. Ilu general, wheu the unalvaient ions on the resin are exchanged with the divalent or the trivalent ions in the solutiac, endothermic behavior is observed and, in the case of exchange xeactious between ions hairing the same ionic valence, the larger the vahues of the sekctivity coefficients the greater the magnitude of the heat of the exothermic exchange reaction. On the basis of this ~~a~~ifi~atio~~[~] it was inferred that the following endothermic and ~~other~~~ reactions occurred simultaneously with shght overall endothermic behavior being observed.

+ c Rh3+ + + [Rh(SO,?

~.I endothermic, 4)]+ i- H+ . . ~ exothermic.

ence is also supported by the result that the apparent molar ratio of the released ions from the resin ts the removed rhodium ions from the soltt

Table 2 shows the elution ratios of the e~.~~a~ged rhodiutn ions on 1 g of

Table 2. Eiution of rhodium ions on the R-H’ with various suihric acid solutions.

-- Acid concentration (N) 4 1 0.5 IO-’

E!ution ratios (%o) 98 70 29 20

solution (cf Table ) with 50 an! 5f IO-” 6 3 sulfuric acid solutions. From Table 2 It cm be see9 that rhodium ions are fully 1 N sulfuric acid, and may be returned direct!y to the rhodium plating sohttion. ( odium plating solutions contain 20 g of rhodium ions and 50 g of sulfuric acid per htre of water.)

From the results it 100 ppm rhodium io that the removed rhodium ious can be e with 1 N sulfuric acid. eluted solu~ior: is re- utilized in the rhodium plating bath. Nit us in waste water cm al reclaimed by almost the same procedure as described for rhodium. owever, to recycle element, it must be treated with calcium hydroxide to neutralize t acid and deposit the excess sulfate ious §~~u~ta~eo~~~y~

Acknowledgement - This work was supported in part by the Grant-in-Aid for Research iron ihe Ministry .3I Education of the Japanese Government. The authors wish to rhank Mrs. Ii. Hatsushika for her secretarial help in the preparation of this paper.

1. T. Suzuki and I’. Hayakawa, Proc. 1st International Congress on Phosphortcs Compounds, 5. 381 I MPHOS Pub., Paris (1977).

2. T. Lcialai~u, T. :~uzuki and H. Kobayashi, 2. chex. Sot. .iir;an 4. 415 (!977). 3. r. S:_xuki and Y. Hayakawa, J. ph_vs. Chem. 4. ‘r. S::zuki and L T. Fan, J. Ferment. Teclmoi., Osaka 57, 578 (1979). 5. T. iuzuki, T. Ha:sushika and Y. Hayakawa, Proc. 2ndinternat~~~nai Congress on Phozphon;s C’u:npcj,tm. ‘3. 162

iMPiiOS Pub., Paris (1980). .5. T. Sczuki, E. Takahashi and Y. Hayakawa, Bunseki Kiki, Jqmn 12, 83 (1974).